sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

netlink: add unregister call in cleanup

For protocols that use netlink (generic and route for now), the unint
handler seems to have forgotten to call unregister, which will cause
the assertion the next time the module is loaded.

This patch adds unregister call to netlink_unregister_proto() for those
handlers to avoid bad things happen.

Reviewed-by: melifaro
Fixes: 7e5bf68495cc ("netlink: add netlink support")
Pull-request: https://github.com/freebsd/freebsd-src/pull/781
Signed-off-by: Lin Ma <linma@zju.edu.cn>

sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

netlink: reduce default log levels

Reduce the default log level for netlink to LOG_INFO. This removes a
number of messages such as

> [nl_iface] dump_sa: unsupported family: 0, skipping
or
> [nl_iface] get_operstate_ether: error calling SIOCGIFMEDIA on vlan0: 22

that are useful for debugging, but not for most users.

Reviewed by: melifaro
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D40062

netlink: allow netlink sockets in non-vnet jails.

This change allow to open Netlink sockets in the non-vnet jails, even for
unpriviledged processes.
The security model largely follows the existing one. To be more specific:
* by default, every `NETLINK_ROUTE` command is **NOT** allowed in non-VNET
jail UNLESS `RTNL_F_ALLOW_NONVNET_JAIL` flag is specified in the command
handler.
* All notifications are **disabled** for non-vnet jails (requests to
subscribe for the notifications are ignored). This will change to be more
fine-grained model once the first netlink provider requiring this gets
committed.
* Listing interfaces (RTM_GETLINK) is **allowed** w/o limits (**including**
interfaces w/o any addresses attached to the jail). The value of this is
questionable, but it follows the existing approach.
* Listing ARP/NDP neighbours is **forbidden**. This is a **change** from the
current approach - currently we list static ARP/ND entries belonging to the
addresses attached to the jail.
* Listing interface addresses is **allowed**, but the addresses are filtered
to match only ones attached to the jail.
* Listing routes is **allowed**, but the routes are filtered to provide only
host routes matching the addresses attached to the jail.
* By default, every `NETLINK_GENERIC` command is **allowed** in non-VNET jail
(as sub-families may be unrelated to network at all).
It is the goal of the family author to implement the restriction if
necessary.

Differential Revision: https://reviews.freebsd.org/D39206
MFC after: 1 month

netlink: add "netlink" to the list of kernel features

Reduce the amount of debug messages on module init/detach.

MFC after: 1 week

netlink: Use NET_EPOCH_[CALL|WAIT] macros

Reviewed by: melifaro, kp
Approved by: kp (mentor)
Differential Revision: https://reviews.freebsd.org/D37730

netlink: add interface notification on link status / flags change.

* Add link-state change notifications by subscribing to ifnet_link_event.
In the Linux netlink model, link state is reported in 2 places: first is
the IFLA_OPERSTATE, which stores state per RFC2863.
The second is an IFF_LOWER_UP interface flag. As many applications rely
on the latter, reserve 1 bit from if_flags, named as IFF_NETLINK_1.
This flag is mapped to IFF_LOWER_UP in the netlink headers. This is done
to avoid making applications think this flag is actually
supported / presented in non-netlink outputs.
* Add flag change notifications, by hooking into rt_ifmsg().
In the netlink model, notification should include the bitmask for the
change flags. Update rt_ifmsg() to include such bitmask.

Differential Revision: https://reviews.freebsd.org/D37597

netlink: remove private netlink_var.h header from the non-netlink core files.

netlink: Fix build without VIMAGE

netlink: add netlink support

Netlinks is a communication protocol currently used in Linux kernel to modify,
read and subscribe for nearly all networking state. Interfaces, addresses, routes,
firewall, fibs, vnets, etc are controlled via netlink.
It is async, TLV-based protocol, providing 1-1 and 1-many communications.

The current implementation supports the subset of NETLINK_ROUTE
family. To be more specific, the following is supported:
* Dumps:
- routes
- nexthops / nexthop groups
- interfaces
- interface addresses
- neighbors (arp/ndp)
* Notifications:
- interface arrival/departure
- interface address arrival/departure
- route addition/deletion
* Modifications:
- adding/deleting routes
- adding/deleting nexthops/nexthops groups
- adding/deleting neghbors
- adding/deleting interfaces (basic support only)
* Rtsock interaction
- route events are bridged both ways

The implementation also supports the NETLINK_GENERIC family framework.

Implementation notes:
Netlink is implemented via loadable/unloadable kernel module,
not touching many kernel parts.
Each netlink socket uses dedicated taskqueue to support async operations
that can sleep, such as interface creation. All message processing is
performed within these taskqueues.

Compatibility:
Most of the Netlink data models specified above maps to FreeBSD concepts
nicely. Unmodified ip(8) binary correctly works with
interfaces, addresses, routes, nexthops and nexthop groups. Some
software such as net/bird require header-only modifications to compile
and work with FreeBSD netlink.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D36002
MFC after: 2 months