[sctp] major surgery to use only SCTP events to determine socket status

• drop concept of on_connected_epoll to determine if socket is ready or not
• provide much better debugging output at all levels
• incorporate fix from Xin Long <lxin@redhat.com> to gather socket status at the right time
• deal with a recent kernel change on SCTP socket that broke knet (from rhel7): [net] sctp: allow delivering notifications after receiving SHUTDOWN

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>