net: dsa: add port fdb dump

Dumping a DSA port's FDB entries is not specific to a DSA slave, so add
a dsa_port_fdb_dump function, similarly to dsa_port_fdb_add and
dsa_port_fdb_del.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 4a98942..02ace7d 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -263,16 +263,11 @@ dsa_slave_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
 	};
 	struct dsa_slave_priv *p = netdev_priv(dev);
 	struct dsa_port *dp = p->dp;
-	struct dsa_switch *ds = dp->ds;
 	int err;
 
-	if (!ds->ops->port_fdb_dump)
-		return -EOPNOTSUPP;
-
-	err = ds->ops->port_fdb_dump(ds, dp->index,
-				     dsa_slave_port_fdb_do_dump,
-				     &dump);
+	err = dsa_port_fdb_dump(dp, dsa_slave_port_fdb_do_dump, &dump);
 	*idx = dump.idx;
+
 	return err;
 }