The minimum amount of time remaining before this entry will
be aged out. If cIpMRouteNextHopState is pruned(1), the
remaining time until the prune expires and the state reverts
to forwarding(2). Otherwise, the remaining time until this
entry is removed from the table. The time remaining may be
copied from cIpMRouteExpiryTime if the protocol in use for
this entry does not specify next-hop timers. The value 0
indicates that the entry is not subject to aging.