s390/qeth: keep track of fixed prio-queue configuration

When a device is configured in prio-queue mode to pin all traffic onto
a specific HW queue, treat this as a distinct variant of prio-queueing
instead of QETH_NO_PRIO_QUEUEING.

This corrects an error message from qeth_osa_set_output_queues() for
devices configured in such a mode.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>