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

[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>