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

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

sys: 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.

[net80211] Begin implementing rate control module stats.

* Implement a new ratectl method, which defaults to returning nothing;
* Add a top level sysctl (net.wlan.X.rate_stats) to extract it;
* Add ratectl info for the 'amrr' module.

Tested:

* urtwn(4), STA mode

Differential Revision: https://reviews.freebsd.org/D5630

Provide includes that are needed in these files, and before were read
in implicitly via if.h -> if_var.h pollution.

Sponsored by: Netflix
Sponsored by: Nginx, Inc.

Instead of using the AMRR ratectl algo as default for drivers which have
the IEEE80211_C_RATECTL flag set, default to NONE for all drivers. Only if
a driver calls ieee80211_ratectl_init() check if the NONE algo is still
selected and try to use AMRR in that case. Drivers are still free to use
any other algo by calling ieee80211_ratectl_set() prior to the
ieee80211_ratectl_init() call.

After this change it is now safe to assume that a ratectl algo is always
available and selected, which renders the IEEE80211_C_RATECTL flag pretty
much useless. Therefore revert r211314 and 211546.

Reviewed by: rpaulo
MFC after: 2 weeks

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Fix an undefined behaviour if the desired ratectl algo is not available.
This can happen if the algos are built as modules but are not loaded. If
the selected ratectl algo is not available, try to load it (The load
module functions does nothing currently). Add a dummy ratectl algo which
always selects the first available rate. Use that one if the desired algo
is not available.

MFC after: 1 week

MFC r206367, r206358, r206370, r206371, r206372, r206398, r206415,
r206416, r206417, r206418, r206418:

net80211 ratectl framework.

net80211 rate control framework (net80211 ratectl).

This framework allows drivers to abstract the rate control algorithm and
just feed the framework with the usable parameters. The rate control
framework will now deal with passing the parameters to the selected
algorithm. Right now we have AMRR (the default) and RSSADAPT but there's
no way to select one with ifconfig, yet.
The objective is to have more rate control algorithms in the net80211
stack so all drivers[0] can use it. Ideally, we'll have the well-known
sample rate control algorithm in the net80211 at some point so all
drivers can use it (not just ath).

[0] all drivers that do rate control in software, that is.

Reviewed by: bschmidt, thompsa, weyongo
MFC after: 1 months