The IP multicast group address which, when combined with
hwPimGroupMappingGrpPrefixLength, gives the group prefix for
this mapping. The InetAddressType is given by the
hwPimGroupMappingAddressType object.
This address object is only significant up to
hwPimGroupMappingGrpPrefixLength bits. The remainder of the
address bits are zero. This is especially important for
this index field, which is part of the index of this entry.
Any non-zero bits would signify an entirely different
entry.