CVE-2026-72229: 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 batadvmeshifvlan on top of it via the NETDEVREGISTER 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 registernetdevice() call will try to clean up the netdevice using unregisternetdevicequeue() - which only uses the .privdestructor to free private resources. In this situation, .dellink will not be called.

The cleanup of the untagged batadvmeshifvlan must thefore be done in the destructor to avoid a leak of this object.