[rbridge] VLAN registration

[Radia Perlman]

Just noticed this section got added to the spec. Some people expressed 
privately to me  (and I share
their concern) a concern that
if RBridges had to support every new feature and protocol that IEEE 
comes up with, that we'll never be finished.
And that at the very least supporting most of these should be MAYs 
rather than MUSTs or even SHOULDs.

As for the VLAN registration frame -- it seems like R2, if it is VLAN x 
forwarder, should only send a VLAN x registration
frame if R2 sees, in its LSP database, that some other RBridge in the 
campus has a VLAN x receiver. If VLAN x is
dynamic, then R2 should not announce VLAN x in its LSP unless there is a 
VLAN x receiver on the link.

If we think that RBridges should be supporting this at all...

Radia