sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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/dev: further 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.

Break out most of the HAL related tweaks into a per-HAL instance,
rather than global variables.

This specifically allows for debugging to be enabled per-NIC, rather
than globally.

Since the ath driver doesn't know about AH_DEBUG, and to keep the ABI
consistent regardless of whether AH_DEBUG is enabled or not, enable the
debug parameter always but only conditionally compile in the debug
methods if needed.

The ALQ support is currently still global pending some brainstorming.

Submitted by: ssgriffonuser@gmail.com
Reviewed by: adrian, bschmidt

Migrate the sysctl related routines (statistics, debugging, etc) out of
if_ath.c and into if_ath_sysctl.c .