net: ethernet: ti: ale: do not auto delete mcast super entries

Do not delete multicast supervisory packet's (SUPER) entries while flushing
multicast addresses from ALE table cpsw_ale_flush_multicast(). Those
entries have to be added/removed only explicitly.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>