new_header
udp = (udphdr_t *)new_header(IPPROTO_UDP);
icmp = (icmphdr_t *)new_header(IPPROTO_ICMP);
new_header(-2);
(void) new_header(-1);
void *new_header(int);
ip = (ip_t *)new_header(IPPROTO_IP);
tcp = (tcphdr_t *)new_header(IPPROTO_TCP);