arp_pln
ah->arp_pln = sizeof(ah->arp_spa); /* protocol address length */
ah->arp_pln != sizeof(ah->arp_spa) )
arp->arp_pln != sizeof(arp->arp_spa) )
ap->arp_pln = sizeof(ap->arp_spa); /* protocol address length */
ap->arp_pln != sizeof(ap->arp_spa) )
ap->arp_hln != 6 || ap->arp_pln != 4) {