WATM — Connection ids in OpenConnection may conflict

In opening a connection for GIOP data (sections 7.2.10--7.2.11) the
receiver of a request is responsible for allocating a connection id.
But if two OpenConnectionRequests cross each other, it might be
possible for the same connection id to be allocated to two different
connections. This would completely break at least one, maybe both, of
the connections.

The easiest way to fix this would be to allocate disjoint subsets of
the available connection id space to Terminal and Access Bridges.
Since this is a question of interoperability, the subsets need to be
also mandated. A good one would be for the Access Bridge to use even
numbers and the Terminal Bridge to use odd numbers (excluding the
invalid 0xffffffff).

Access Bridge uses even numbers and Terminal Bridge odd numbers (but not 0xFFFFFFFF).