The value of vRtrIgmpIfMcacLagLevel specifies the level id to use
when the value of tmnxMcacLagPortsDown matches the actual number
of ports down in a lag.
Using the value of vRtrIgmpIfMcacLagLevel as an index, the
operational interface unconstrained bandwidth will be set to
vRtrIgmpIfMcacLevelBW.
By default for all lag constraints the interface level will be
set to 1 at row creation.