- Add a macro to compute the max frame length based on Ethertype
and presence of FCS, and use it to validate the packet size
in ether_input().
- Add capabilites to struct ethercom, and allow hardware drivers
to specify that they can handle the larger hardware MTU that
VLANs require in order to strictly conform to 802.1Q.
- Make ether_ifdetach() clear out the link address and free all of
the Ethernet multicast structures.
Also, rearrange the VLAN driver itself in preparation to supporting
other hardware types, including FDDI (which has 802.1Q VLAN capability).
