netfilter: nf_flow_table_path: L2 bridge offload

This series adds L2 bridge offload support to nft_flow_offload, allowing
bridged IPv4/IPv6 flows to be accelerated by the flowtable fast path
without requiring L3 routing.

Background
----------
Hardware flow offload engines (e.g. MediaTek PPE) can accelerate bridged
traffic but require that nft_flow_offload detect and handle bridged flows
differently from routed ones: no routing table lookup, MAC addresses from
the Ethernet header, and VLAN context pre-populated from the bridge port.

Patches
-------
1/5  net: export __dev_fill_forward_path
     Refactors dev_fill_forward_path() to expose __dev_fill_forward_path()
     which accepts a caller-supplied net_device_path_ctx, needed to
     pre-populate VLAN state before the forward path walk.

2/5  net: bridge: add flow offload helpers
     Adds br_fdb_has_forwarding_entry_rcu(), br_vlan_get_offload_info_rcu()
     and br_vlan_is_enabled_rcu() to expose bridge state to nft_flow_offload
     without requiring inclusion of net/bridge/br_private.h.

3/5  netfilter: nf_flow_table_path: add L2 bridge offload
     Core of the series. Adds nft_flow_offload_is_bridging() detection,
     nft_flow_route_bridging() which avoids nf_route() (fails for
     bridged-only subnets), MAC/VLAN pre-population for bridged flows,
     and a dst leak fix (allocation references in dsts[] were never
     released after nft_default_forward_path() transferred ownership).
     nft_flow_route() becomes a thin dispatcher.

4/5  netfilter: nf_flow_table_path: handle DEV_PATH_MTK_WDMA in path info
     Fixes zero-source-MAC in PPE entries when a bridged flow traverses
     MT7996/MT7915 WiFi WDMA hardware.

5/5  netfilter: nf_flow_table_path: add VLAN passthrough support
     Records VLAN encap info for passthrough-mode bridge ports so hardware
     offload entries include the correct VLAN tag.

Rebase note
-----------
Originally developed against OpenWrt pending-6.18 patches by Ryan Chen
<rchen14b@gmail.com> and Bo-Cun Chen <bc-bocun.chen@mediatek.com>.
Rebased to current upstream: path discovery infrastructure moved to
nf_flow_table_path.c in commit 93d7a7ed0734 ("netfilter: flowtable: move
path discovery infrastructure to its own file"), so all netfilter changes
now land in that file rather than nft_flow_offload.c.

How to enable bridge offload
-----------------------------
1. Load kmod-br-netfilter so that bridged IP traffic traverses the
   netfilter forward chain.

2. Enable netfilter hooks on the bridge:
     echo 1 > /sys/class/net/<br>/bridge/nf_call_iptables
     echo 1 > /sys/class/net/<br>/bridge/nf_call_ip6tables

3. Register bridge member interfaces in the nft flowtable:
     table inet filter {
         flowtable f {
             hook ingress priority filter
             devices = { eth0, wlan0 }
         }
         chain forward {
             type filter hook forward priority filter
             meta l4proto { tcp, udp } flow add @f
         }
     }

Daniel Pawlik (1):
  net: bridge: add flow offload helpers

Ryan Chen (4):
  net: export __dev_fill_forward_path
  netfilter: nf_flow_table_path: add L2 bridge offload
  netfilter: nf_flow_table_path: handle DEV_PATH_MTK_WDMA in path info
  netfilter: nf_flow_table_path: add VLAN passthrough support

 include/linux/if_bridge.h          |  23 ++++
 include/linux/netdevice.h          |   2 +
 net/bridge/br_fdb.c                |  32 +++++
 net/bridge/br_vlan.c               |  45 +++++++
 net/core/dev.c                     |  32 +++--
 net/netfilter/nf_flow_table_path.c | 201 +++++++++++++++++++++++++++--
 6 files changed, 312 insertions(+), 23 deletions(-)

-- 
2.54.0