net: mediatek: do not set the QID field in the TX DMA descriptors

The QID field gets set to the mac id. This made the DMA linked list queue
the traffic of each MAC on a different internal queue. However during long
term testing we found that this will cause traffic stalls as the multi
queue setup requires a more complete initialisation which is not part of
the upstream driver yet.

This patch removes the code setting the QID field, resulting in all
traffic ending up in queue 0 which works without any special setup.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>