The value of vRtrPimNgIfGrpSrcDataMtIfIndex indicates the interface
index of the Multicast Tunnel(MT) interface. If the value of
vRtrPimNgIfGrpSrcDataMtIfIndex is zero, it indicates that there is no
data MT associated with this group-source interface to forward
multicast traffic into the service provider network. If the
value of vRtrPimNgIfGrpSrcDataMtIfIndex is non-zero, it indicates the
data MT tunnel that is used to forward multicast traffic into the
service provider network.