netfilter: nf_tables: bogus EBUSY when deleting flowtable after flush (for 5.4)

3f0465a9ef02 ("netfilter: nf_tables: dynamically allocate hooks per
net_device in flowtables") reworks flowtable support to allow for
dynamic allocation of hooks, which implicitly fixes the following
bogus EBUSY in transaction:

  delete flowtable
  add flowtable # same flowtable with same devices, it hits EBUSY

This patch does not exist in any tree, but it fixes this issue for
-stable Linux kernel 5.4

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/netfilter/nf_tables_api.c

@@ -6132,6 +6132,9 @@ static int nf_tables_newflowtable(struct net *net, struct sock *nlsk,
 			continue;
 
 		list_for_each_entry(ft, &table->flowtables, list) {
+			if (!nft_is_active_next(net, ft))
+				continue;
+
 			for (k = 0; k < ft->ops_len; k++) {
 				if (!ft->ops[k].dev)
 					continue;