IP_RECVIF
*mp = sbcreatecontrol(&sdl, sdl.sdl_len, IP_RECVIF, IPPROTO_IP);
case IP_RECVIF:
case IP_RECVIF:
case IP_RECVIF:
case IP_RECVIF:
CASERETURN(IP_RECVIF);
if (setsockopt(s, IPPROTO_IP, IP_RECVIF, &(uint32_t){1},
cmptr->cmsg_type == IP_RECVIF) {