Fix some bugs in RECEIVE COPY STATUS data.

MFC after:	3 days
Plug EXTENDED COPY request data memory leak.

MFC after:	3 days
Fix a copy and paste error.

X-MFC with: 269436
Add support for the SCTP_PR_SUPPORTED socket option as specified in
http://tools.ietf.org/html/draft-ietf-tsvwg-sctp-prpolicies
Add also a sysctl controlling the default of the end-points.

MFC after: 1 week
Rework r269444 to work also for lists without IDs.

MFC after:	3 days
Add myself to committers-src.dot.
Better late than never :-)
Remove Giant acquisition from the mount and unmount pathes.

It could be claimed that two things were reasonable protected by
Giant.  One is vfsconf list links, which is converted to the new
dedicated sx vfsconf_sx.  Another is vfsconf.vfc_refcount, which is
now updated with atomics.

Note that vfc_refcount still has the same races now as it has under
the Giant, the unload of filesystem modules can happen while the
module is still in use.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Do the iwn(4) panic reinitialisation under IWN_LOCK().

I've checked each of the functions being called and there's either a
_locked version or it's supposed to be called with IWN_LOCK() held.
Make the witness lock limit an option.
Add required `exec' before Xdialog(1) invocation for the case where we
expect (require) data on stdin. The effect of this is that, when
backgrounded, $! returns the pid of an Xdialog(1) instance instead of
an sh(1) instance -- the difference being a later kill of $! will reach
the Xdialog(1) instance whereas without the exec the kill succeeds on
the sh(1) instance leaving Xdialog(1) open.
vn_path_to_global_path: update comment.
Revert r269404 and use cpu_ticks() for dbuf allocation.

Encode CPU's number by XOR'ing the CPU ID against the 64-bit cpu_ticks().

Reviewed by:	mav, gibbs
Differential Revision: https://phabric.freebsd.org/D521
MFC after:	2 weeks
Do not retry token errors. They are not going to disappear by themselves.

MFC after:	1 week
Avoid a divide-by-zero panic when setting the baudrate to 0.

MFC after:	2 weeks
Fix vt_vga driver to draw not-8-bit-aligned fonts correctly.
Still one bug here: mouse left some gaps on track when moving left.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Do not retry on set of non-transient XCOPY errors.

MFC after:	1 week
Allow to disable some special key combinations handled by vt(4), like debug
request, reboot request.

Requested by:	Claude Buisson

Sponsored by:	The FreeBSD Foundation
Add SCTP socket option SCTP_NRSACK_SUPPORTED to control the
NRSACK extension. The default will still be off, since it
it not an RFC (yet).
Changing the sysctl name will be in a separate commit.

MFC after: 1 week
Use consistent names for SCTP sysctls. Rename
nr_sack_on_off to nrsack_enable.
Please note that this extension is off by default
since it is not specified in an RFC (yet).
Fix multicast, broken by the conversion of the nfe(4) driver to the
driver API.

Submitted by:	Mikhail <mp@lenta.ru>