ip_fragment
error = ip_fragment(m, &ml, ifp, ifp->if_mtu);
if (ip_fragment(m0, &ml, ifp, ifp->if_mtu) ||
if ((error = ip_fragment(m, &ml, ifp, mtu)) ||
int ip_fragment(struct mbuf *, struct mbuf_list *, struct ifnet *, u_long);