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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

IfAPI: Add l2com accessor for firewire.

Summary:
Firewire is the only device driver that accesses the l2com member, all
other accesses are handled within the netstack itself.

Sponsored by: Juniper Networks, Inc.
Reviewed by: glebius, melifaro
Differential Revision: https://reviews.freebsd.org/D38203

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.

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

Switch cmd argument to u_long. This matches what if_ethersubr.c does and
allows the code to compile cleanly on amd64 with clang.

Reviewed by: rwatson
Approved by: ed (mentor)

- Import the HEAD csup code which is the basis for the cvsmode work.

Stop embedding struct ifnet at the top of driver softcs. Instead the
struct ifnet or the layer 2 common structure it was embedded in have
been replaced with a struct ifnet pointer to be filled by a call to the
new function, if_alloc(). The layer 2 common structure is also allocated
via if_alloc() based on the interface type. It is hung off the new
struct ifnet member, if_l2com.

This change removes the size of these structures from the kernel ABI and
will allow us to better manage them as interfaces come and go.

Other changes of note:
- Struct arpcom is no longer referenced in normal interface code.
Instead the Ethernet address is accessed via the IFP2ENADDR() macro.
To enforce this ac_enaddr has been renamed to _ac_enaddr.
- The second argument to ether_ifattach is now always the mac address
from driver private storage rather than sometimes being ac_enaddr.

Reviewed by: sobomax, sam

Fix big-endian build.

Add a new driver to support IP over firewire. This driver is intended to
conform to the rfc2734 and rfc3146 standard for IP over firewire and
should eventually supercede the fwe driver. Right now the broadcast
channel number is hardwired and we don't support MCAP for multicast
channel allocation - more infrastructure is required in the firewire
code itself to fix these problems.