atl1c: do MAC-reset when PHY link down

There may be tx-skbs still pending in HW when PHY link down.
Reset MAC will make the DMA engine go to the start point.
and release all pending skbs.
Note: Reset MAC will clear any interrupt status and mask.

Signed-off-by: xiong <xiong@qca.qualcomm.com>
Tested-by: Liu David <dwliu@qca.qualcomm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>