icmp_nextmtu
ntohs(icp->icmp_nextmtu));
u_long mtu = ntohs(icp->icmp_nextmtu); /* Why a long? IPv6 */
icp->icmp_nextmtu = htons(destmtu);
mtu = (u_int)ntohs(icp->icmp_nextmtu);
tp->t_pmtud_nextmtu = icp->icmp_nextmtu;
icmp.icmp_nextmtu = tp->t_pmtud_nextmtu;
icp->icmp_nextmtu = htons(destmtu);
pmtu = ntohs(icp->icmp_nextmtu);
nextmtu = ntohs(icp->icmp_nextmtu); /* for frag_err() */