qeth: don't query for info if hardware not ready.

When qeth device is queried for ethtool data, hardware operation
is performed to extract the necessary information from the card.
If the card is not online at the moment (e.g. it is undergoing
recovery), this operation produces undesired effects like
temporarily freezing the system. This patch prevents execution
of the hardware query operation when the card is not online.
In such case, ioctl() operation returns error with errno ENODEV.

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