[rbridge] Consensus Check: Configure ports to disable end station traffic

[Eastlake III Donald-LDE008]

This is a check via the mailing list to confirm or refute an apparent
consensus at the Vancouver meeting taken from the minutes of that
meeting:

           Currently broadcast, unknown unicast, and
      non-IP-derived multicast frames are output to all links. This is
      wasteful if there are no end stations on the link. Provide that
      a port can be configured so as to be disabled for end station
      traffic.

If no particular controversy arises over this in the next three weeks,
We will declare it to be the working group consensus.

Thanks,
Donald & Erik