pffindproto
prp = pffindproto(dom, proto, type);
pr = pffindproto(PF_INET, IPPROTO_RAW, SOCK_RAW);
pr = (const struct ip6protosw *)pffindproto(PF_INET6, IPPROTO_RAW, SOCK_RAW);
const struct protosw *pffindproto(int, int, int);