net: ethernet: mtk_eth_soc: implement flow offloading to WED devices

This allows hardware flow offloading from Ethernet to WLAN on MT7622 SoC

Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David S. Miller <davem@davemloft.net>