Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Merge r247666, r247712, r247811.

Fix ipfw table argument parsing/printing.
Fix style.

PR: kern/175909
Submitted by: Daniel Hagerty <hag@linnaean.org>

Implement buffer size checking in ipfw(8) add cmd.

PR: bin/65961
Submitted by: Eugene Grosbein <eugen@grosbein.pp.ru>

Do not suddenly fail on some rulesets if -n (syntax check only) is specified
and ipfw(4) module is not loaded.

Merge r240892,r240893

Permit table to be used as IPv6 address.
Whitespace fixes

Reported by: Serhiy Popov <sergiuspso@ukr.net>

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Whitespace fixes.

Checked with: md5, diff -w

Put nat and ipv6 support in their own files.

Usual moving of code with no changes from ipfw2.c to the
newly created files, and addition of prototypes to ipfw2.h

I have added forward declarations for ipfw_insn_* in ipfw2.h
to avoid a global dependency on ip_fw.h