net: dsa: use switchdev obj in port_fdb_del

For consistency with the FDB add operation, propagate the
switchdev_obj_port_fdb structure in the DSA drivers.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>