batman-adv: don't access unregistered net_device object

In batadv_hardif_disable_interface() there is a call to
batadv_softif_destroy_sysfs() which in turns invokes
unregister_netdevice() on the soft_iface.
After this point we cannot rely on the soft_iface object
anymore because it might get free'd by the netdev periodic
routine at any time.

For this reason the netdev_upper_dev_unlink(.., soft_iface) call
is moved before the invocation of batadv_softif_destroy_sysfs() so
that we can be sure that the soft_iface object is still valid.
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

net/batman-adv/hard-interface.c

@@ -528,6 +528,8 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface,
 	batadv_purge_outstanding_packets(bat_priv, hard_iface);
 	dev_put(hard_iface->soft_iface);
 
+	netdev_upper_dev_unlink(hard_iface->net_dev, hard_iface->soft_iface);
+
 	/* nobody uses this interface anymore */
 	if (!bat_priv->num_ifaces) {
 		batadv_gw_check_client_stop(bat_priv);
@@ -536,7 +538,6 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface,
 			batadv_softif_destroy_sysfs(hard_iface->soft_iface);
 	}
 
-	netdev_upper_dev_unlink(hard_iface->net_dev, hard_iface->soft_iface);
 	hard_iface->soft_iface = NULL;
 	batadv_hardif_free_ref(hard_iface);