qeth: display "undefined" value of sysfs-attribute "layer2"

If nothing has been written into the qeth sysfs-attribute layer2,
its value is "-1" meaning "not yet defined". But the value is
displayed as "1" meaning "layer2 selected". The patch changes the
reading of this "-1"-value to "-1" to make clear the layer2-attribute
has not yet been defined.

Signed-off-by: Ursula Braun <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/s390/net/qeth_core_sys.c

···
 	if (!card)
 		return -EINVAL;
 
-	return sprintf(buf, "%i\n", card->options.layer2 ? 1:0);
+	return sprintf(buf, "%i\n", card->options.layer2);
 }
 
 static ssize_t qeth_dev_layer2_store(struct device *dev,