net: dsa: add port_fdb_prepare

Push the prepare phase for FDB operations down to the DSA drivers, with
a new port_fdb_prepare function. Currently only mv88e6xxx is affected.

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>
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 4f607bc..48e8c15 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -346,10 +346,13 @@
 {
 	struct dsa_slave_priv *p = netdev_priv(dev);
 	struct dsa_switch *ds = p->parent;
-	int ret = -EOPNOTSUPP;
+	int ret;
+
+	if (!ds->drv->port_fdb_prepare || !ds->drv->port_fdb_add)
+		return -EOPNOTSUPP;
 
 	if (switchdev_trans_ph_prepare(trans))
-		ret = ds->drv->port_fdb_add ? 0 : -EOPNOTSUPP;
+		ret = ds->drv->port_fdb_prepare(ds, p->port, fdb, trans);
 	else
 		ret = ds->drv->port_fdb_add(ds, p->port, fdb->addr, fdb->vid);