Do not put any link-layer address on the per-ifp lists or on the RB-

Do not put any link-layer address on the per-ifp lists or on the RB-
Tree.

Since interfaces only support one link-layer address accessible via the
if_sadl member, there's no need to have it elsewhere.  This improves
various address lookups because the first element of the list, the link-
layer address, won't necessarily be discarded.

Finally remove the empty netmask associated to every link-layer address.
This hack was needed to (ab)use the address & netmask comparison code to
do a strcmp() on the interface name embedded in the sdl_data field.

ok henning@, claudio@