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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

New Netgraph module ng_macfilter:

Macfilter to route packets through different hooks based on sender MAC address.

Based on ng_macfilter written by Pekka Nikander

Sponsered by Retina b.v.

Reviewed by: afedorov
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D27268