MFC r351134: Add support for 'j', 't' and 'z' flags to kernel sscanf().

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

sys/kern: spelling fixes in comments.

No functional change.

Xen netback driver rewrite.

share/man/man4/Makefile,
share/man/man4/xnb.4,
sys/dev/xen/netback/netback.c,
sys/dev/xen/netback/netback_unit_tests.c:

Rewrote the netback driver for xen to attach properly via newbus
and work properly in both HVM and PVM mode (only HVM is tested).
Works with the in-tree FreeBSD netfront driver or the Windows
netfront driver from SuSE. Has not been extensively tested with
a Linux netfront driver. Does not implement LRO, TSO, or
polling. Includes unit tests that may be run through sysctl
after compiling with XNB_DEBUG defined.

sys/dev/xen/blkback/blkback.c,
sys/xen/interface/io/netif.h:

Comment elaboration.

sys/kern/uipc_mbuf.c:

Fix page fault in kernel mode when calling m_print() on a
null mbuf. Since m_print() is only used for debugging, there
are no performance concerns for extra error checking code.

sys/kern/subr_scanf.c:

Add the "hh" and "ll" width specifiers from C99 to scanf().
A few callers were already using "ll" even though scanf()
was handling it as "l".

Submitted by: Alan Somers <alans@spectralogic.com>
Submitted by: John Suykerbuyk <johns@spectralogic.com>
Sponsored by: Spectra Logic
MFC after: 1 week
Reviewed by: ken

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

Approved by: core

Use __FBSDID().

Deprecate machine/limits.h in favor of new sys/limits.h.
Change all in-tree consumers to include <sys/limits.h>

Discussed on: standards@
Partially submitted by: Craig Rodrigues <rodrigc@attbi.com>

Fix mis-indentation.

Spotted by: FlexeLint

Change the prototype of the strto* routines to make the second
parameter a char ** instead of a const char **. This make these
kernel routines consistent with the corresponding libc userland
routines.

Which is actually 'correct' is debatable, but consistency and
following the spec was deemed more important in this case.

Reviewed by (in concept): phk, bde

Move strto{u}[ql]() into their own libkern files.

Urged by: bde

Move isfoo() and friends to the newly created sys/ctype.h.

Urged by: bde

Consolidate some of the various ctype(3) macros in one location.

Add strtol & strtoul to kernel. Derived from libc versions.

Trim unused options (or #ifdef for undoc options).

Submitted by: phk

$Id$ -> $FreeBSD$

Cast pointers to uintptr_t instead of casting them to u_long, and/or vice
versa. Cosmetic.

Only needed to cast array index from char to unsigned char, did not
also have to cast it to int. (int)(unsigned char)char_exp ->
(unsigned char)char_exp.

cleanup warnings by propogating const char pointers properly.

Fix warnings in preparation for adding -Wall -Wcast-qual to the
kernel compile

Fix array index of signed char to cast to unsigned char and then to int.
Also general const cleanup.

Add sscanf/vsscanf/strtoq/strtouq to the kernel. Initially these will be used
for parsing kernel environment values, although they have utility elsewhere.