kernel: allow adding devices without hw offload to a hw flowtable

This allows supporting a mix of devices with or without hw offloading support

Signed-off-by: Felix Fietkau <[email protected]>
(cherry picked from commit c5b7be8)

target/linux/generic/pending-5.15/701-netfilter-nf_tables-ignore-EOPNOTSUPP-on-flowtable-d.patch

@@ -0,0 +1,29 @@
+From: Felix Fietkau <[email protected]>
+Date: Thu, 31 Aug 2023 21:48:38 +0200
+Subject: [PATCH] netfilter: nf_tables: ignore -EOPNOTSUPP on flowtable device
+ offload setup
+
+On many embedded devices, it is common to configure flowtable offloading for
+a mix of different devices, some of which have hardware offload support and
+some of which don't.
+The current code limits the ability of user space to properly set up such a
+configuration by only allowing adding devices with hardware offload support to
+a offload-enabled flowtable.
+Given that offload-enabled flowtables also imply fallback to pure software
+offloading, this limitation makes little sense.
+Fix it by not bailing out when the offload setup returns -EOPNOTSUPP
+
+Signed-off-by: Felix Fietkau <[email protected]>
+---
+
+--- a/net/netfilter/nf_tables_api.c
++++ b/net/netfilter/nf_tables_api.c
+@@ -7729,7 +7729,7 @@ static int nft_register_flowtable_net_ho
+ 		err = flowtable->data.type->setup(&flowtable->data,
+ 						  hook->ops.dev,
+ 						  FLOW_BLOCK_BIND);
+-		if (err < 0)
++		if (err < 0 && err != -EOPNOTSUPP)
+ 			goto err_unregister_net_hooks;
+
+ 		err = nf_register_net_hook(net, &hook->ops);