ipv4cksum
extern uint16_t ipv4cksum(uint16_t *, uint16_t);
icmphp->icmp_cksum = ipv4cksum((uint16_t *)icmphp,
if (ipv4cksum((uint16_t *)icmphp, icmp_len) != 0) {
iphp->ip_sum = ipv4cksum((uint16_t *)iphp, sizeof (struct ip));
iph->ip_sum = ipv4cksum((uint16_t *)iph, sizeof (struct ip));
if (ipv4cksum((uint16_t *)iphp, iphlen) != 0) {