net: ethernet: mtk_eth_soc: support creating mac address based offload entries

This will be used to implement a limited form of bridge offloading.
Since the hardware does not support flow table entries with just source
and destination MAC address, the driver has to emulate it.

The hardware automatically creates entries entries for incoming flows, even
when they are bridged instead of routed, and reports when packets for these
flows have reached the minimum PPS rate for offloading.

After this happens, we look up the L2 flow offload entry based on the MAC
header and fill in the output routing information in the flow table.
The dynamically created per-flow entries are automatically removed when
either the hardware flowtable entry expires, is replaced, or if the offload
rule they belong to is removed

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David S. Miller <davem@davemloft.net>