mlxsw: spectrum_switchdev: Flood mc when mc is disabled by user flag

When multicast is disabled, flood mc packets only to port that are marked
BR_MCAST_FLOOD (instead to all).

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>