net: dsa: Change DSA slave FDB API to be switchdev independent

In order to support FDB add/del to be on a notifier chain the slave
API need to be changed to be switchdev independent.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>