qeth: fix qeth_wait_for_threads() deadlock for OSN devices

Any recovery thread will deadlock when calling qeth_wait_for_threads(), most
notably when triggering a recovery on an OSN device.
This patch will store the recovery thread's task pointer on recovery
invocation and check in qeth_wait_for_threads() respectively to avoid
deadlocks.

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Reviewed-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>