netfilter: nfnetlink_log: fix silly refcount leak

Quick fix for memory/module refcount leak.
Reference count of listener instance never reaches 0.

Start/stop of ulogd2 is enough to trigger this bug!

Now, refcounting there looks very fishy in particular this code:

 	if (!try_module_get(THIS_MODULE)) {
		...

and creation of listener instance with refcount 2,
so it may very well be ripped and redone.  :-)
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nfnetlink_log.c

@@ -768,7 +768,7 @@ nfulnl_recv_config(struct sock *ctnl, struct sk_buff *skb,
 			}
 
 			instance_destroy(inst);
-			goto out;
+			goto out_put;
 		default:
 			ret = -ENOTSUPP;
 			break;