Add support for "timeo", "actimeo", "noac", and "proto" options
to mount_nfs(8).  They are implemented on Linux, OS X, and Solaris,
and thus can be expected to appear in automounter maps.

Reviewed by:	rmacklem@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Fix a race condition in TCP timewait between tcp_tw_2msl_reuse() and
tcp_tw_2msl_scan().  This race condition drives unplanned timewait
timeout cancellation.  Also simplify implementation by holding inpcb
reference and removing tcptw reference counting.

Differential Revision:	https://reviews.freebsd.org/D826
Submitted by:		Marc De la Gueronniere <mdelagueronniere@verisign.com>
Submitted by:		jch
Reviewed By:		jhb (mentor), adrian, rwatson
Sponsored by:		Verisign, Inc.
MFC after:		2 weeks
X-MFC-With:		r264321