The value of vRtrMldIfGrpSrcAddress indicates the address of the
source sending multicast traffic to the group identified by
vRtrMldIfGroupAddress.
If the value of vRtrMldIfGroupMode corresponding to this entry is
'include', the receivers are interested in receiving traffic
from this source.
If the value of vRtrMldIfGroupMode corresponding to this entry is
'exclude' and if the value of vRtrMldIfGrpSrcExpiryTime is '0',
the receivers are not interested in receiving traffic from this
source.