Add a family-independent bindresvport_sa function

Add a family-independent bindresvport_sa function

This functions allows you to pass IPv4 and IPv6 addresses.  If no
address is given, t will determine the family by checking the socket
with getsockname.

[ghudson@mit.edu: clarified commit message, split out setport helper,
squashed with next commit, minimized code changes from old
bindresvport, used socket-utils.h helpers]

ticket: 7935 (new)