[S390] cio: provide fake irb for transport mode IO

If a driver wants to do command mode IO while CIO is doing
online path verification we ignore this request and provide
a fake irb when we are done and the driver can do IO again.

For transport mode IO we have no such mechanism, giving the
driver no other chance then to retry the action until we are
done. This is not very reliable.

Provide a fake irb for transport mode IO as well.

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