The peer from which an SA message corresponding to this
cache entry would be accepted (i.e. the RPF peer for
cMsdpSACacheOriginRP). This may be different than
cMsdpSACachePeerLearnedFrom if this entry was created by an
MSDP SA-Response. This address must correspond to the
cMsdpPeerRemoteAddress value for a row in the MSDP Peer
Table, or may be 0.0.0.0 if no RPF peer exists.