[BPQ] lockdep: fix false positive

Bpqether is encapsulating AX.25 frames into ethernet frames.  There is a
virtual bpqether device paired with each ethernet devices, so it's normal
to pass through dev_queue_xmit twice for each frame which triggers the
locking detector.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/bpqether.c

@@ -122,6 +122,12 @@ struct bpqdev {
 
 static LIST_HEAD(bpq_devices);
 
+/*
+ * bpqether network devices are paired with ethernet devices below them, so
+ * form a special "super class" of normal ethernet devices; split their locks
+ * off into a separate class since they always nest.
+ */
+static struct lock_class_key bpq_netdev_xmit_lock_key;
 
 /* ------------------------------------------------------------------------ */
 
@@ -528,6 +534,7 @@ static int bpq_new_device(struct net_device *edev)
 	err = register_netdevice(ndev);
 	if (err)
 		goto error;
+	lockdep_set_class(&ndev->_xmit_lock, &bpq_netdev_xmit_lock_key);
 
 	/* List protected by RTNL */
 	list_add_rcu(&bpq->bpq_list, &bpq_devices);