net: airoha: Add l2_flows rhashtable

Introduce l2_flows rhashtable in airoha_ppe struct in order to
store L2 flows committed by upper layers of the kernel. This is a
preliminary patch in order to offload L2 traffic rules.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Link: https://patch.msgid.link/20250409-airoha-flowtable-l2b-v2-1-4a1e3935ea92@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>