* Don't call ifp->if_output() from inside mpls_output(). Make the

* Don't call ifp->if_output() from inside mpls_output(). Make the
  caller responsible for sending the packet.

* Fix mpls gateway arp resoving.

* Introduce a new mbuf flag M_MPLSLABELED indicating that the packet
  has at least one valid mpls label on it.

* Use the new mbuf flag instead of forging a sockaddr_mpls to let
  ether_output() identify the mpls packets.

* Drop the packet when mpls ttl is exceeded (doesn't send an ICMP message yet).

* Fix compilation warning.

* Improve comments.