Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Fix socket buffer timeouts precision using the new sbintime_t KPI instead
of relying on the tvtohz() workaround. The latter has been introduced
lately by jhb@ (r254699) in order to have a fix that can be backported
to STABLE.

Reported by: Vitja Makarov <vitja.makarov at gmail dot com>
Reviewed by: jhb (earlier version)

Add missing socket options.

Remove extra 'comma = 0' in socket state printing code, which otherwise
could lead to an extra comma in output.

Submitted by: Christoph Mallon <christoph dot mallon at gmx dot de>

s/SS_FDREF/SS_NOFDREF/

Remove two further uses (debugging and NULLing) of pr_ousrreq, missed due
to svn commit in the wrong directory.

Spotted by: bz

Change a variable name to not shadow a global

Obtained from: vimage

Add missing sb_sndptr* fields to db_print_sockbuf().
While here change %d to %u for u_ints.

Discussed with: rwatson, kmacy

sblock() implements a sleep lock by interlocking SB_WANT and SB_LOCK flags
on each socket buffer with the socket buffer's mutex. This sleep lock is
used to serialize I/O on sockets in order to prevent I/O interlacing.

This change replaces the custom sleep lock with an sx(9) lock, which
results in marginally better performance, better handling of contention
during simultaneous socket I/O across multiple threads, and a cleaner
separation between the different layers of locking in socket buffers.
Specifically, the socket buffer mutex is now solely responsible for
serializing simultaneous operation on the socket buffer data structure,
and not for I/O serialization.

While here, fix two historic bugs:

(1) a bug allowing I/O to be occasionally interlaced during long I/O
operations (discovere by Isilon).

(2) a bug in which failed non-blocking acquisition of the socket buffer
I/O serialization lock might be ignored (discovered by sam).

SCTP portion of this patch submitted by rrs.

Teach DDB how to print sockets, socket buffers, protosw's, and domain
structures given pointers to them.