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

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Add a complete implementation of MurmurHash3. Tweak both implementations
so they match the established idiom. Document them in hash(9).

MFC after: 1 month
MFC with: r272906

Change the PF hash from Jenkins to Murmur3. In forwarding tests
this showed a conservative 3% incrase in PPS.

Differential Revision: https://reviews.freebsd.org/D461
Submitted by: des
Reviewed by: emaste
MFC after: 1 month

- Move jenkins.h to jenkins_hash.c
- Provide missing function that can do hashing of arbitrary sized buffer.
- Refetch lookup3.c and do only minimal edits to it, so that diff between
our jenkins_hash.c and lookup3.c is minimal.
- Add declarations for jenkins_hash(), jenkins_hash32() to sys/hash.h.
- Document these functions in hash(9)

Obtained from: http://burtleburtle.net/bob/c/lookup3.c

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

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

Fix a compiler warning so hash.h can be included in the kernel. This changes
the args for hash32_stre and hash32_strne but there are no consumers in the
base system and openbgpd does not use it which the initial import was for.

Silence on: hackers

Remove comment that does not appy to FreeBSD.

Import of OpenBSD's sys/sys/hash.h providing generic 32bit hash functions.

Requested by: flz (to port Open[BGP|OSPF]D)
MFC after: 3 days