s390/qeth: handle error due to unsupported transport mode

Along with z/VM NICs, there's additional device types that only support
a specific transport mode (eg. external-bridged IQD).
Identify the corresponding error code, and raise a fitting error message
so that the user knows to adjust their device configuration.

On top of that also fix the subsequent error path, so that the rejected
cmd doesn't need to wait for a timeout but gets cancelled straight away.

Fixes: 4a71df50 ("qeth: new qeth device driver")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>