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

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

Upgrade (almost) to natd 2.0b1

- Transparent proxy support.
- PERMANENT_LINK IS NOW OBSOLETE, use redirect_port instead.
- Drop support for early FreeBSD 2.2 versions
- If separate input & output sockets are being used
use them to find out packet direction instead of
normal mechanism. This can be handy in complex environments
with multiple interfaces.
- PPTP redirect support by Dru Nelson <dnelson@redwoodsoft.com> added.
- Logging enhancements from Martin Machacek <mm@i.cz> added.

Obtained from: Ari Suutari <ari@suutari.iki.fi>

natd 1_10 => 1_11
Cosmetic style changes
Use u_short for port values.
Submitted by: Ari Suutari <ari@suutari.iki.fi>

Ingored incoming packets are now dropped when
deny_incoming option is set to yes.
Submitted by: Ari Suutari <ari@suutari.iki.fi>

- Buffer space problem found by Sergio Lenzi <lenzi@bsi.com.br>
fixed. Natd now waits with select(2) for buffer space
to become available if write fails.
- Packet aliasing library upgraded to 2.2.

Submitted by: Ari Suutari <suutari@iki.fi>