ipf: Use nitems(foo) instead of sizeof(foo)/sizeof(foo[0])

Pull Request: https://github.com/freebsd/freebsd-src/pull/888
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>

Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

ipf: Use C89 function definitions.

Reviewed by: zlei
Differential Revision: https://reviews.freebsd.org/D39523

ipfilter userland: Style(9) requires a space after return

Reported by: jrtc27
Fixes: 2582ae5740181e0d2bab10003d66ae91c9b56329
MFC after: 1 month

ipfilter: Adjust userland returns to conform to style(9)

Adjust ipfilter's userland return statements to conform to style(9).

MFC after: 1 month

ipflter: ANSIfy userland function declarations

Convert ipfilter userland function declarations from K&R to ANSI. This
syncs our function declarations with NetBSD hg commit 75edcd7552a0
(apply our changes). Though not copied from NetBSD, this change was
partially inspired by NetBSD's work and inspired by style(9).

Reviewed by: glebius (for #network)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D33595

ipfilter: Move userland bits to sbin

Through fixes and improvements our ipfilter sources have diverged
enough to warrant move from contrib into sbin/ipf. Now that I'm
planning on implementing MSS clamping as in iptables it makes more
sense to move ipfilter to sbin.

This is the second of three commits of the ipfilter move.

Suggested by glebius on two occaions.

Suggested by and discussed with: glebius
Reviewed by: glebius, kp (for #network)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D33510