dpaa2-eth: fix race condition with bql frame accounting

It might happen that Tx conf acknowledges a frame before it was
subscribed in bql, as subscribing was previously done after the enqueue
operation.

This patch moves the netdev_tx_sent_queue call before the actual frame
enqueue, so that this can never happen.

Fixes: 569dac6a ("dpaa2-eth: bql support")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>