Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Rationalize BSD license on sys/*/include/in_cksum.h

Remove the advertising clause from the Regents of the University of
California's license, per the letter dated July 22, 1999.

Update clause numbering.

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

Sync with the other archs and wrapper the prototype of in_cksum_skip(9)
in #ifdef _KERNEL.

Submitted by: Ulrich Spoerlein
MFC after: 1 month

Revert the addition of "__volatile" to "__asm" done in r180011, since
the condition codes where added to the clobber lists in r180073 the
former is unnecessary.

Improve r180011 by explicitly adding the condition codes to the
clobber list.

Suggested by: Christoph Mallon

Use "__asm __volatile" rather than "__asm" for instruction sequences
that modify condition codes (the carry bit, in this case). Without
"__volatile", the compiler might add the inline assembler instructions
between unrelated code which also uses condition codes, modifying the
latter.
This prevents the TCP pseudo header checksum calculation done in
tcp_output() from having effects on other conditions when compiled
with GCC 4.2.1 at "-O2" and "options INET6" left out. [1]

Reported & tested by: Boris Kochergin [1]
MFC after: 3 days

- The inline asm in this file uses output operands before all input
operands are consumed so use the appropriate constraint modifier.
Before this change GCC used one register for both an input and an
unrelated output operand of in_addword(), causing the input to be
overwritten before it was consumed and thus breaking in_addword().
For in_cksum_hdr() and in_pseudo() this change is more or less
cosmetic.
- Fix a misspelling in a nearby comment.

Reported & tested by: yongari
MFC after: 1 week

Remove advertising clause from University of California Regent's
license, per letter dated July 22, 1999 and email from Peter Wemm,
Alan Cox and Robert Watson.

Approved by: core, peter, alc, rwatson

Add optimized implementations of in_cksum_skip() and related functions
for sparc64.