icmp_nextmtu
if (ntohs(icmp->icmp_nextmtu) != 0) {
ntohs(icmp->icmp_nextmtu));
if (icmp->icmp_nextmtu < ifs->ifs_fr_icmpminfragmtu)
icmp->icmp_nextmtu = net_getmtu(ifs->ifs_ipf_ipv4, phy,0 );