netfilter: nftables: fix possible double hook unregistration with table owner

Skip hook unregistration of owner tables from the netns exit path,
nft_rcv_nl_event() unregisters the table hooks before tearing down
the table content.

Fixes: 6001a930 ("netfilter: nftables: introduce table ownership")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -9028,8 +9028,12 @@ static void __nft_release_hooks(struct net *net)
 {
 	struct nft_table *table;
 
-	list_for_each_entry(table, &net->nft.tables, list)
+	list_for_each_entry(table, &net->nft.tables, list) {
+		if (nft_table_has_owner(table))
+			continue;
+
 		__nft_release_hook(net, table);
+	}
 }
 
 static void __nft_release_table(struct net *net, struct nft_table *table)