s390/qeth: reshuffle initialization

Reshuffle the init function of the qeth driver to ensure
that the driver is usable at the time it is registered.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>