MFC 265253:
Don't treat TRIM requests returning ENOTSUP as an unexpected error

Approved by:	re (gjb)
Sponsored by:	Multiplay
MFC virtio-net changes.

Re-tested with NetBSD/amd64 5.2.2, 6.1.4 and 7-beta.

r271299:
Add a callback to be notified about negotiated features.

r271338:
Allow vtnet operation without merged rx buffers.

NetBSD's virtio-net implementation doesn't negotiate
the merged rx-buffers feature. To support this, check
to see if the feature was negotiated, and then adjust
the operation of the receive path accordingly by using
a larger iovec, and a smaller rx header.
In addition, ignore writes to the (read-only) status byte.

Approved by:	re (glebius)
Obtained from:	Vincenzo Maffione, Universita` di Pisa (r271299)
Bump __FreeBSD_version after SA-14:19.tcp

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
Document SA-14:19

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
MFC r270160:

Destroy the "qdiffsample_zone" UMA zone on unload to avoid a use-after-unload
panic easily triggered by running "sysctl -a" after unload.

Reported and tested by:	Grenville Armitage <garmitage@swin.edu.au>
Approved by:	re(gjb)
Merge remote-tracking branch 'freebsd/stable/10' into hardened/10/aslr