netfilter: xt_hashlimit: dl_seq_stop() fix

If dl_seq_start() memory allocation fails, we crash later in
dl_seq_stop(), trying to kfree(ERR_PTR(-ENOMEM))
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/xt_hashlimit.c

@@ -879,7 +879,8 @@ static void dl_seq_stop(struct seq_file *s, void *v)
 	struct xt_hashlimit_htable *htable = s->private;
 	unsigned int *bucket = (unsigned int *)v;
 
-	kfree(bucket);
+	if (!IS_ERR(bucket))
+		kfree(bucket);
 	spin_unlock_bh(&htable->lock);
 }