bridge: fix a possible net_device leak

Jan Beulich reported a possible net_device leak in bridge code after
commit bb900b27a2f4 (bridge: allow creating bridge devices with netlink)

Reported-by: Jan Beulich <JBeulich@novell.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_if.c

@@ -231,6 +231,7 @@ static struct net_bridge_port *new_nbp(struct net_bridge *br,
 int br_add_bridge(struct net *net, const char *name)
 {
 	struct net_device *dev;
+	int res;
 
 	dev = alloc_netdev(sizeof(struct net_bridge), name,
 			   br_dev_setup);
@@ -240,7 +241,10 @@ int br_add_bridge(struct net *net, const char *name)
 
 	dev_net_set(dev, net);
 
-	return register_netdev(dev);
+	res = register_netdev(dev);
+	if (res)
+		free_netdev(dev);
+	return res;
 }
 
 int br_del_bridge(struct net *net, const char *name)