net: ethernet: mtk_eth_soc: add support for configuring vlan rx offload

Keep the vlan rx offload feature in sync across all netdevs belonging to the
device, since the feature is global and can't be turned off per MAC

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>