The value of vRtrMldIfGroupMode is based on the type of
membership report(s) received on the interface for the group.
In the 'include' mode, reception of packets sent to the
specified multicast address is requested only from those
IP source addresses listed in the source-list parameter of
the MLD membership report.
In 'exclude' mode, reception of packets sent to the given
multicast address is requested from all IP source addresses
except those listed in the source-list parameter.
vRtrMldIfGrpSrcTable lists the sources corresponding to this group,
if any.