sctp_mtu_payload
return sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT, datasize);
int frag = sctp_mtu_payload(sctp_sk(asoc->base.sk), asoc->pathmtu,
packet->overhead = sctp_mtu_payload(sp, 0, 0);
size = sctp_mtu_payload(sp, size, sizeof(struct sctp_errhdr));