sctp: Select a working primary during sctp_connectx()

When sctp_connectx() is used, we pick the first address as
primary, even though it may not have worked.  This results
in excessive retransmits and poor performance.  We should
select the address that the association was established with.

Reported-by: Thomas Dreibholz <dreibh@iem.uni-due.de>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>