packet_ok
i = packet_ok(packet, cc, from, seq);
int packet_ok(u_char *, int, struct sockaddr_in *, int);
int packet_ok(struct msghdr *, int, int, u_char *, u_char *, u_char *);
if (packet_ok(&rcvmhdr, cc, seq, &type, &code, &ecn)) {