s390/qeth: don't reset default_out_queue

When an OSA device in prio-queue setup is reduced to 1 TX queue due to
HW restrictions, we reset its the default_out_queue to 0.

In the old code this was needed so that qeth_get_priority_queue() gets
the queue selection right. But with proper multiqueue support we already
reduced dev->real_num_tx_queues to 1, and so the stack puts all traffic
on txq 0 without even calling .ndo_select_queue.

Thus we can preserve the user's configuration, and apply it if the OSA
device later re-gains support for multiple TX queues.

Fixes: 73dc2daf ("s390/qeth: add TX multiqueue support for OSA devices")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>