mlxsw: spectrum_switchdev: Use generic mc flood function

Use the generic mc flood function to decide whether to flood mc to a port
when mc is being enabled / disabled.
Move this function in the file to avoid forward declaration.

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>