netfilter: nf_tables: Keep deleted flowtable hooks until after RCU

Documentation of list_del_rcu() warns callers to not immediately free
the deleted list item. While it seems not necessary to use the
RCU-variant of list_del() here in the first place, doing so seems to
require calling kfree_rcu() on the deleted item as well.

Fixes: 3f0465a ("netfilter: nf_tables: dynamically allocate hooks per net_device in flowtables")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -9207,7 +9207,7 @@ static void nf_tables_flowtable_destroy(struct nft_flowtable *flowtable)
 		flowtable->data.type->setup(&flowtable->data, hook->ops.dev,
 					    FLOW_BLOCK_UNBIND);
 		list_del_rcu(&hook->list);
-		kfree(hook);
+		kfree_rcu(hook, rcu);
 	}
 	kfree(flowtable->name);
 	module_put(flowtable->data.type->owner);