This is a unique index for an entry in the
MplsInterfaceConfTable. A non-zero index for an
entry indicates the ifIndex for the corresponding
interface entry in of the MPLS-layer in the ifTable.
Note that the per-platform label space may apply to
several interfaces, and therefore the configuration
of the per-platform label space interface parameters
will apply to all of the interfaces that are
participating in the per-platform label space.