The minimum amount of time remaining before this entry will
be aged out.
If the value of vRtrIgmpHostGrpSrcExpiryTime is non-zero and the
value of vRtrIgmpIfGroupMode corresponding to this entry is 'include',
it means that there are currently one or more systems which desire
to receive multicast traffic for this source. If this timer expires
and the value of vRtrIgmpIfGroupMode is 'include', the router
concludes that traffic from this particular source is no longer
desired on the attached network, and deletes this entry.
This timer is treated differently when the value of vRtrIgmpIfGroupMode
is 'exclude'. If the value of vRtrIgmpHostGrpSrcExpiryTime is non-zero
and router filter-mode for the group is 'exclude', it means that at
least one system desires to receive multicast traffic from this source.
It should therefore be forwarded by a router on the network.