qeth: provide specific message for OSA-adapters exclusively used

Exclusive usage of OSA-cards has been introduced. Even though Linux
does not make use of it, qeth should be prepared to receive a bad RC
for some initialization steps. A meaningful message is now given,
if an OSA-device is set online, even though the OSA-adapter is already
exclusively used by another host.

Signed-off-by: Ursula Braun <braunu@de.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>