net: dsa: do not warn unsupported bridge ops

A DSA driver may not provide the port_join_bridge and port_leave_bridge
functions, so don't warn in such case.
Signed-off-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -1276,7 +1276,7 @@ int dsa_slave_netdevice_event(struct notifier_block *unused,
 			goto out;
 
 		err = dsa_slave_master_changed(dev);
-		if (err)
+		if (err && err != -EOPNOTSUPP)
 			netdev_warn(dev, "failed to reflect master change\n");
 
 		break;