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

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

Remove alignment constraints.

Retire the MALLOC and FREE macros. They are an abomination unto style(9).

MFC after: 3 months

Update ip and tcp pointers after m_pullup().

Submitted by: Alexander Motin <mav alkar.net>

Free private data when deleting hook.

PR: kern/93952
Submitted by: Antoine Brodin <antoine.brodin laposte.net>

- Remove redundant parenthesis in M_CHECK macro.
- Do not edit pullup_len outside M_CHECK macro.
- Do not reimplement NG_FWD_NEW_DATA().
- Remove redundant check for item being not NULL.

Submitted by: ru

Add ng_tcpmss node, which alters MSS options of TCP packets. Useful to
hack MSS of packets outgoing via interface with small MTU, to workaround
path MTU discovery problems.

Written by Alexey Popov, with some cleanups from me. There are also plans
to improve mpd port, so that it uses this node, instead of doing MSS
hacking in userland, when 'enable tcpmssfix' option is on.

Submitted by: Alexey Popov <lollypop@flexuser.ru>