[AX25]: Make sure and hold ref to dev.

The lower layers of ax25 hold a reference to the underlying device
but don't increment the ref count. This is safe because it does the
right thing when UNREGISTER notification comes in, but it is better
to do the right thing.

net/ax25/ax25_dev.c

@@ -67,6 +67,7 @@ void ax25_dev_device_up(struct net_device *dev)
 
 	dev->ax25_ptr     = ax25_dev;
 	ax25_dev->dev     = dev;
+	dev_hold(dev);
 	ax25_dev->forward = NULL;
 
 	ax25_dev->values[AX25_VALUES_IPDEFMODE] = AX25_DEF_IPDEFMODE;
@@ -121,6 +122,7 @@ void ax25_dev_device_down(struct net_device *dev)
 	if ((s = ax25_dev_list) == ax25_dev) {
 		ax25_dev_list = s->next;
 		spin_unlock_bh(&ax25_dev_lock);
+		dev_put(dev);
 		kfree(ax25_dev);
 		ax25_register_sysctl();
 		return;
@@ -130,6 +132,7 @@ void ax25_dev_device_down(struct net_device *dev)
 		if (s->next == ax25_dev) {
 			s->next = ax25_dev->next;
 			spin_unlock_bh(&ax25_dev_lock);
+			dev_put(dev);
 			kfree(ax25_dev);
 			ax25_register_sysctl();
 			return;
@@ -196,8 +199,8 @@ void __exit ax25_dev_free(void)
 	ax25_dev = ax25_dev_list;
 	while (ax25_dev != NULL) {
 		s        = ax25_dev;
+		dev_put(ax25_dev->dev);
 		ax25_dev = ax25_dev->next;
-
 		kfree(s);
 	}
 	ax25_dev_list = NULL;