sys: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

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

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

machine/in_cksum.h: don't include sys/cdefs.h

All consumers already do it and it was required on amd64 and i386
until recently (1c1bf5bd7c1e479a7889839b941f53e689aa2569).

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D34932

netinet: Deduplicate most in_cksum() implementations

in_cksum() and related routines are implemented separately for each
platform, but only i386 and arm have optimized versions. Other
platforms' copies of in_cksum.c are identical except for style
differences and support for big-endian CPUs.

Deduplicate the implementations for the rest of the platforms. This
will make it easier to implement in_cksum() for unmapped mbufs. On arm
and i386, define HAVE_MD_IN_CKSUM to mean that the MI implementation is
not to be compiled.

No functional change intended.

Reviewed by: kp, glebius
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33095

sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

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.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Delete stray clause 3 and renumber.

trim trailing whitespace

MFp4 bz_ipv6_fast:

in_cksum.h required ip.h to be included for struct ip. To be
able to use some general checksum functions like in_addword()
in a non-IPv4 context, limit the (also exported to user space)
IPv4 specific functions to the times, when the ip.h header is
present and IPVERSION is defined (to 4).

We should consider more general checksum (updating) functions
to also allow easier incremental checksum updates in the L3/4
stack and firewalls, as well as ponder further requirements by
certain NIC drivers needing slightly different pseudo values
in offloading cases. Thinking in terms of a better "library".

Sponsored by: The FreeBSD Foundation
Sponsored by: iXsystems

Reviewed by: gnn (as part of the whole)
MFC After: 3 days

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.

MFp4: Forget the asm inlined version of in_cksum_hdr(). It doesn't work if
the pointer is unaligned, and it just doesn't worth it.

asm versions of in_cksum_hdr() and in_pseudo().

Use asm versions of in_cksum() and friends.

Import FreeBSD/arm kernel bits.
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.