HOOK_RDONLY
ipst->ips_ip4_nic_events.he_flags = HOOK_RDONLY;
ipst->ips_ip4_observe.he_flags = HOOK_RDONLY;
ipst->ips_ip6_nic_events.he_flags = HOOK_RDONLY;
ipst->ips_ip6_observe.he_flags = HOOK_RDONLY;