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

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

New netgraph node ng_patch(4). It performs data modification of packets
passing through. Modifications are restricted to a subset of C language
operations on unsigned integers of 8, 16, 32 or 64 bit size.
These are: set to new value (=), addition (+=), subtraction (-=),
multiplication (*=), division (/=), negation (= -), bitwise AND (&=),
bitwise OR (|=), bitwise eXclusive OR (^=), shift left (<<=),
shift right (>>=). Several operations are all applied to a packet
sequentially in order they were specified by user.

Submitted by: Maxim Ignatenko <gelraen.ua at gmail.com>
Vadim Goncharov <vadimnuclight at tpu.ru>
Discussed with: net@
Approved by: mav (mentor)
MFC after: 1 month