net: ethernet: mtk_eth_soc: enable special tag when any MAC uses DSA

The special tag is only enabled when the first MAC uses DSA. However, it
must be enabled when any MAC uses DSA. Change the check accordingly.

This fixes hardware DSA untagging not working on the second MAC of the
MT7621 and MT7623 SoCs, and likely other SoCs too. Therefore, remove the
check that disables hardware DSA untagging for the second MAC of the MT7621
and MT7623 SoCs.

Fixes: a1f47752 ("net: ethernet: mtk_eth_soc: disable hardware DSA untagging for second MAC")
Co-developed-by: Richard van Schagen <richard@routerhints.com>
Signed-off-by: Richard van Schagen <richard@routerhints.com>
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Signed-off-by: David S. Miller <davem@davemloft.net>