sctps_initial_mtu
sctp->sctp_mss = sctps->sctps_initial_mtu - ((family == AF_INET6) ?
fp->sf_ssthresh = sctps->sctps_initial_mtu;
(sctps->sctps_initial_mtu - sctp->sctp_hdr_len) &
(sctps->sctps_initial_mtu - sctp->sctp_hdr6_len) &