batman-adv: clean untagged VLAN on netdev registration failure

In the Linux kernel, the following vulnerability has been resolved: batman-adv: clean untagged VLAN on netdev registration failure When an mesh interface is registered, it creates an untagged struct batadv_meshif_vlan on top of it via the NETDEV_REGISTER notifier. But in this process, another receiver of this notification can veto the registration. The netdev registration will be aborted because of this veto. The register_netdevice() call will try to clean up the net_device using unregister_netdevice_queue() - which only uses the .priv_destructor to free private resources. In this situation, .dellink will not be called. The cleanup of the untagged batadv_meshif_vlan must thefore be done in the destructor to avoid a leak of this object.