pfil_head_create
if_pfil = pfil_head_create(PFIL_TYPE_IFNET, NULL);
ifp->if_pfil = pfil_head_create(PFIL_TYPE_IFNET, ifp);
pfil_head_t * pfil_head_create(int, void *);
inet_pfil_hook = pfil_head_create(PFIL_TYPE_AF, (void *)AF_INET);
inet6_pfil_hook = pfil_head_create(PFIL_TYPE_AF, (void *)AF_INET6);