net: lan966x: Fix when a port's upper is changed.

On lan966x it is not allowed to have foreign interfaces under a bridge
which already contains lan966x ports. So when a port leaves the bridge
it would call switchdev_bridge_port_unoffload which eventually will
notify the other ports that bridge left the vlan group but that is not
true because the bridge is still part of the vlan group.

Therefore when a port leaves the bridge, stop generating replays because
already the HW cleared after itself and the other ports don't need to do
anything else.

Fixes: cf2f6089 ("net: lan966x: Add support to offload the forwarding.")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/lan966x/lan966x_switchdev.c

@@ -322,8 +322,7 @@ static int lan966x_port_prechangeupper(struct net_device *dev,
 
 	if (netif_is_bridge_master(info->upper_dev) && !info->linking)
 		switchdev_bridge_port_unoffload(port->dev, port,
-						&lan966x_switchdev_nb,
-						&lan966x_switchdev_blocking_nb);
+						NULL, NULL);
 
 	return NOTIFY_DONE;
 }