The value of vRtrPimNgGrpSrcRslvdByRtTblType indicates which
unicast routing table was used to resolve this source group entry.
The value of this object will be 'mucastRouteTable' if the
source or rendezvous point (RP) is resolved by the multicast-unicast
route table. The value of this object will be 'ucastRouteTable' if
the source or rendezvous point (RP) is resolved by the unicast
route table. The value will be 'none' if the source or RP is
unresolved.