When the Alder Lake Serial-over-LAN device is put into loopback mode and
repeated writes are performed to the data register it results in the device
ending up in a broken state.
The way to recover the device requires draining the Receiver queue ahead of
waiting for the device to drain it's transmit queue. Doing in that
specific order fixes the device. Also note that the draining and flushing
of the queues should better be done unconditionally, hence place it inside
the describe label so it's also done when exiting early from the FIFO
length testing loop.