net: ethernet: mtk_eth_soc: drop generic vlan rx offload, only use DSA untagging

Through testing I found out that hardware vlan rx offload support seems to
have some hardware issues. At least when using multiple MACs and when
receiving tagged packets on the secondary MAC, the hardware can sometimes
start to emit wrong tags on the first MAC as well.

In order to avoid such issues, drop the feature configuration and use
the offload feature only for DSA hardware untagging on MT7621/MT7622
devices where this feature works properly.

Fixes: 08666cbb7dd5 ("net: ethernet: mtk_eth_soc: add support for configuring vlan rx offload")
Tested-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Link: https://lore.kernel.org/r/20230426172153.8352-1-linux@fw-web.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>