protosw_register
error = protosw_register(&inetdomain, &sctp_stream_protosw);
error = protosw_register(&inetdomain, &sctp_seqpacket_protosw);
error = protosw_register(&inet6domain, &sctp6_stream_protosw);
error = protosw_register(&inet6domain, &sctp6_seqpacket_protosw);
error = protosw_register(&inet6domain, &send_protosw);
int protosw_register(struct domain *, struct protosw *);