Add support for send, receive and state-change DTrace providers for
SCTP. They are based on what is specified in the Solaris DTrace manual
for Solaris 11.4.

Reviewed by: 0mp, dteske, markj
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D16839

- Remove hardcoded paths for the perl executable.
- Rather than assuming that a process is listening on 127.0.0.1:22, use
nc(1) to find an available port and bind to it for the duration of the
test.

MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division

Convert a couple of helper scripts used to test the ip provider to work on
FreeBSD. In the IPv6 case, try each interface before returning an error;
each IPv6-enabled interface will have a link-local address even if the link
isn't up.

MFC after: 1 week

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Port most of the DTrace tests to FreeBSD.

Sponsored by: The FreeBSD Foundation