Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

o Create directory sys/netpfil, where all packet filters should
reside, and move there ipfw(4) and pf(4).

o Move most modified parts of pf out of contrib.

Actual movements:

sys/contrib/pf/net/*.c -> sys/netpfil/pf/
sys/contrib/pf/net/*.h -> sys/net/
contrib/pf/pfctl/*.c -> sbin/pfctl
contrib/pf/pfctl/*.h -> sbin/pfctl
contrib/pf/pfctl/pfctl.8 -> sbin/pfctl
contrib/pf/pfctl/*.4 -> share/man/man4
contrib/pf/pfctl/*.5 -> share/man/man5

sys/netinet/ipfw -> sys/netpfil/ipfw

The arguable movement is pf/net/*.h -> sys/net. There are
future plans to refactor pf includes, so I decided not to
break things twice.

Not modified bits of pf left in contrib: authpf, ftp-proxy,
tftp-proxy, pflogd.

The ipfw(4) movement is planned to be merged to stable/9,
to make head and stable match.

Discussed with: bz, luigi

Ignore the return value of ADDCARRY().

Use in_cksum_skip() to calculate in4_cksum instead of doing handrolled magic
(that does not compile with !gcc). Moreover we get the benefit for all archs
that have a hand optimized in_cksum_skip().

Submitted by: yongari
Tested by: me (i386, extensivly), pf4freebsd ML (various)

Commit pf version 3.5 and link additional files to the kernel build.

Version 3.5 brings:
- Atomic commits of ruleset changes (reduce the chance of ending up in an
inconsistent state).
- A 30% reduction in the size of state table entries.
- Source-tracking (limit number of clients and states per client).
- Sticky-address (the flexibility of round-robin with the benefits of
source-hash).
- Significant improvements to interface handling.
- and many more ...

Bring diff from the security/pf port. This has code been tested as a port
for a long time and is run in production use. This is the code present in
portversion 2.03 with some additional tweaks.

The rather extensive diff accounts for:
- locking (to enable pf to work with a giant-free netstack)
- byte order difference between OpenBSD and FreeBSD for ip_len/ip_off
- conversion from pool(9) to zone(9)
- api differences etc.

Approved by: bms(mentor) (in general)

This commit was generated by cvs2svn to compensate for changes in r126258,
which included commits to RCS files with non-trunk default branches.

Vendor import of OpenBSD's packet filter (pf) as of OpenBSD 3.4

Approved by: bms(mentor), core (in general)