net: ethernet: mtk_eth_soc: add foe_entry_size to mtk_eth_soc

Introduce foe_entry_size to mtk_eth_soc data structure since mt7986
relies on a bigger mtk_foe_entry data structure.

Tested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>