carp: support VRRPv3

Allow carp(4) to use the VRRPv3 protocol (RFC 5798). We can distinguish carp and
VRRP based on the protocol version number (carp is 2, VRRPv3 is 3), and support
both from the carp(4) code.

Reviewed by: glebius
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D44774

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

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

ifconfig: remove global 'name' variable.

Consistenly use newly-added 'ctx->ifname' as the name of the current
target interface.

Reviewed By: kp
Differential Revision: https://reviews.freebsd.org/D40438
MFC after: 2 weeks

ifconfig: eliminate global 'verbose' and 'printkey' variables

Reviewed By: kp
Differential Revision: https://reviews.freebsd.org/D40427
MFC after: 2 weeks

ifconfig: add if_ctx argument to the generic and ifclone callbacks.

This is the continuation of the ifconfig cleanup work. This change is
a pre-requsite for the next changes removing some of the global variables.
It will also help in implementing functionality via Netlink instead of ioctl.
No functional changes intended.
* vxlan_cb() was removed as it contained no code
* ioctl_ifcreate() was renamed to ifcreate_ioctl() to follow the other
netlink/ioctl function naming. Netlink and ioctl provide _different_
interfaces and it's not possible to have a unified interface object
that can be filled by either netlink or ioctl implementations. With that
in mind, I'm leaning more to the function_<nl|ioctl> postfix pattern,
than doing ioctl_ or netlink_ prefix.

Reviewed By: kp
Differential Revision: https://reviews.freebsd.org/D40426
MFC after: 2 weeks

ifconfig: fix warnings #2

Fix all -Wparameter-unused and cast alignment

Differential Revision: https://reviews.freebsd.org/D40303
MFC after: 2 weeks

ifconfig: introduce `ifconfig_context` to store current global state.

The structure consists of all current context - arguments,
open sockets, current family and so on.

Pass this structure as a first argument to most of the af_ menthods.
This allows to propagate and update shared data without using
global variables.

The diff is pretty large, but de-facto mechanical. All changes
except the structure setup in ifconfig[_netlink].c are one-line
mechanical changes.

Reviewed by: kp
Differential Revision: https://reviews.freebsd.org/D40239
MFC after: 2 weeks

ifconfig: cleanup warnings #1

Cleanup compiler warnings in preparation to set Wextra and remove WARNS?=2

Differential Revision: https://reviews.freebsd.org/D40238
MFC after: 2 weeks

ifconfig: simplify carp vhid setup.

Currently carp implementation peeks into the opaque 'afp->af_addreq'
buffer, assumes it knows the af-specific layout and assigns vhid
directly.
Simplify the code and remove abstraction leak by introducing per-afp
callback for setting vhid.
This change is a pre-requisite to set addresses via Netlink,
as Netlink implementiation uses different structure layout.

Reviewed by: kp
Differential Revision: https://reviews.freebsd.org/D40160
MFC after: 2 weeks

ifconfig: improve error checking for carp peer6

getaddrinfo() returns 0 if it succeeded, but it's not guaranteed to
return 1 on error. Check for success rather than for one specific error.

Without this fix commands such as `ifconfig bnxt1 inet6 add vhid 1 peer6
2001:db8::1/64` would segfault ifconfig.

Sponsored by: Rubicon Communications, LLC ("Netgate")

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

ifconfig: change carp commands mcast and mcast6 to DEF_CMD as they take no args

Reviewed by: kp
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D39548

ifconfig: free memory allocated by getaddrinfo()

Reported by: emaste, Coverity
Sponsored by: Rubicon Communications, LLC (Netgate)

carp: support unicast

Allow users to configure the address to send carp messages to. This
allows carp to be used in unicast mode, which is useful in certain
virtual configurations (e.g. AWS, VMWare ESXi, ...)

Reviewed by: melifaro
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D38940

carp: add netlink interface

Allow carp configuration information to be supplied and retrieved via
netlink.

Reviewed by: melifaro
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D39048

sbin/ifconfig: Use a global libifconfig handle

This should eventually replace the socket passed to the various
handlers. In the meantime, making it global avoids repeatedly opening
and closing handles.

Reported by: kp
Reviewed by: kp (earlier version)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D28990

sbin/ifconfig: Get carp status with libifconfig

A trivial change now that ifconfig is already using libifconfig.
Reviewed by: kp (earlier version)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D28955

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Replace N #defines with nitems to simplify ifconfig code slightly

MFC after: 1 week

Stop including if_var.h from userland.

Sponsored by: Nginx, Inc.

Rename ifcarp.c to carp.c