lagg_gethdr
static const void *lagg_gethdr(struct mbuf *, u_int, u_int, void *);
vlan = lagg_gethdr(m, off, sizeof(*vlan), &buf);
ip = lagg_gethdr(m, off, sizeof(*ip), &buf);
ports = lagg_gethdr(m, off, sizeof(*ports), &buf);
ip6 = lagg_gethdr(m, off, sizeof(*ip6), &buf);