[rbridge] Consensus Check: V-field reversion

[Eastlake III Donald-LDE008]

This is a check via the mailing list to confirm or refute an apparent
consensus at the Chicago meeting for a change from protocol draft -05:

   Eliminate different V field values and revert to two version bits
   and two reserved bits with the previous provisions that this draft
   specifies version zero, frames with an unknown version are
   discarded, reserved bits MUST be zero and are ignored on receipt.

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

Thanks,
Donald & Erik