add: udp_in.sin_family = AF_INET;
context: static void udp_init(void){	udb.inp_prev = udb.inp_next = &udb;	udp_sendspace = 9216; /* default size */	udp_recvspace = 41600; /* default size */	udp_in.sin_len = sizeof(udp_in);	memset(&udpstat, 0, sizeof(udpstat));			memset(proto, 0, sizeof(struct protosw *) * IPPROTO_MAX);	add_protosw(proto, NET_LAYER2);}