The value of tmnxPimSnpgIfGrpSrcJPRptState indicates the Join Prune
Rpt state for this entry on the interface. PIM Join or Prune messages
are sent by the downstream routers towards the RPF' neighbor.
(S,G,rpt) state is a result of receiving (S,G, rpt) JP message from
the downstream router on the RP tree.