The maximum number of VCI Bits that may
currently be used at this ATM interface.
The value is the minimum of
atmInterfaceMaxActiveVciBits, and the
atmInterfaceMaxActiveVciBits of the interface's
UNI/NNI peer.
If the interface does not negotiate with
its peer to determine the number of VCI Bits
that can be used on the interface, then the
value of this object must equal
atmInterfaceMaxActiveVciBits.