Phonet: remove useless locking in device cleanup

Incoming packets and sockets are already gone.
The netdevice notifier is unregistered under the RTNL lock
There remains a race with the rtnetlink handlers unregistration, but it
is a generic RTNL issue that was already present before this change.
Signed-off-by: NRémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/phonet/pn_dev.c

@@ -204,13 +204,8 @@ void phonet_device_exit(void)
 	struct phonet_device *pnd, *n;
 
 	rtnl_unregister_all(PF_PHONET);
-	rtnl_lock();
-	spin_lock_bh(&pndevs.lock);
+	unregister_netdevice_notifier(&phonet_device_notifier);
 
 	list_for_each_entry_safe(pnd, n, &pndevs.list, list)
 		__phonet_device_free(pnd);
-
-	spin_unlock_bh(&pndevs.lock);
-	rtnl_unlock();
-	unregister_netdevice_notifier(&phonet_device_notifier);
 }