MFC r221249:

MFC r221249:
Improve compilation of SCTP code without INET support.
Some bugs where fixed while doing this:
* ASCONF-ACK messages might use wrong port number when using
  IPv6.
* Checking for additional addresses takes the correct address
  into account and also does not do more comparisons than
  necessary.

This patch is based on one received from bz@ who was
sponsored by The FreeBSD Foundation and iXsystems.

git-svn-id: svn://svn.freebsd.org/base/stable/8@231426 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f