The recently updated ALE APIs cpsw_ale_del_mcast() and
cpsw_ale_del_vlan_modify() have an issue and will not delete ALE entry even
if VLAN/mcast group has no more members. Hence fix it here and delete ALE
entry if !port_mask.

The issue affected only new cpsw switchdev driver.

Fixes: e85c1437 ("net: ethernet: ti: ale: modify vlan/mdb api for switchdev")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>