netfilter: nf_tables: prohibit deletion of a table with existing sets

We currently leak the set memory when deleting a table that still has
sets in it. Return EBUSY when attempting to delete a table with sets.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_tables_api.c

···
 	if (IS_ERR(table))
 		return PTR_ERR(table);
 
-	if (table->use)
+	if (!list_empty(&table->chains) || !list_empty(&table->sets))
 		return -EBUSY;
 
 	list_del(&table->list);