tmnxOamMcastTrRespPrevHopRtrAddr specifies the router from which this
router expects packets from this source. This may be a multicast
group (e.g. ALL-[protocol]-ROUTERS.MCAST.NET) if the previous hop is
not known because of the workings of the multicast routing protocol.
This object was obsoleted in release 4.0 and replaced with
InetAddress objects tmnxOamMcastTrRespPhRtrAddrType and
tmnxOamMcastTrRespPhRtrAddress.