mlxsw: spectrum: Update mc_disabled flag by switchdev attr

Add a function to update mc_disabled from switchdev attr
SWITCHDEV_ATTR_ID_BRIDGE_MC_DISABLED

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