net: bridge: vlan: fix single net device option dumping

When dumping vlan options for a single net device we send the same
entries infinitely because user-space expects a 0 return at the end but
we keep returning skb->len and restarting the dump on retry. Fix it by
returning the value from br_vlan_dump_dev() if it completed or there was
an error. The only case that must return skb->len is when the dump was
incomplete and needs to continue (-EMSGSIZE).
Reported-by: Benjamin Poirier <bpoirier@nvidia.com>
Fixes: 8dcea187 ("net: bridge: vlan: add rtm definitions and dump support")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_vlan.c

@@ -2020,7 +2020,8 @@ static int br_vlan_rtm_dump(struct sk_buff *skb, struct netlink_callback *cb)
 			goto out_err;
 		}
 		err = br_vlan_dump_dev(dev, skb, cb, dump_flags);
-		if (err && err != -EMSGSIZE)
+		/* if the dump completed without an error we return 0 here */
+		if (err != -EMSGSIZE)
 			goto out_err;
 	} else {
 		for_each_netdev_rcu(net, dev) {