It can happen that SCTP communication is simply lost, e.g.

  [SCTP]   SCTP_ASSOC_CHANGE to SCTP_COMM_LOST
  [SCTP]   sctp_recvmsg (fd 104, len -1 ): Connection reset by peer:104

The previous code only handled the SHUTDOWN event, but in abnormal
situations, we should also handle the connection state change and signal
to RRC that the endpoint is dead, which is now implemented.