net: dsa: qca8k: make sure PAD0 MAC06 exchange is disabled

net: dsa: qca8k: make sure PAD0 MAC06 exchange is disabled

Some device set MAC06 exchange in the bootloader. This cause some
problem as we don't support this strange mode and we just set the port6
as the primary CPU port. With MAC06 exchange, PAD0 reg configure port6
instead of port0. Add an extra check and explicitly disable MAC06 exchange
to correctly configure the port PAD config.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Fixes: 52ec49c332ad ("net: dsa: qca8k: add support for cpu port 6")
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>