The value of vRtrPimNgAFGenMvpnCMcastSignal specifies which protocol
to use, BGP or PIM, for PE-to-PE signaling of CE multicast states.
When vRtrPimNgAFGenMvpnCMcastSignal is set to 'pim' and neighbor
discovery via BGP is disabled, PIM peering will be enabled on the
inclusive tree.