sctp_sendmsg
extern int sctp_sendmsg(struct sctp_s *conn, mblk_t *mp, int flags);
error = sctp_sendmsg((struct sctp_s *)ssa->ssa_conn, mctl, 0);
error = sctp_sendmsg((struct sctp_s *)so->so_proto_handle, mctl, 0);
extern ssize_t sctp_sendmsg(int, const void *, size_t, const struct sockaddr *,
extern ssize_t sctp_sendmsg();