selftests: refactor get_netdev_name function

As pointed out by Michal Kubecek, getting the name
with the previous approach was racy, it's better
and easier to get the name of the device with this
patch's approach.

Essentialy the function doesn't need to exist
anymore as it's a simple 'ls' command.
Signed-off-by: NAntonio Cardace <acardace@redhat.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/netdevsim/ethtool-common.sh

@@ -20,23 +20,6 @@ function cleanup {
 
 trap cleanup EXIT
 
-function get_netdev_name {
-    local -n old=$1
-
-    new=$(ls /sys/class/net)
-
-    for netdev in $new; do
-	for check in $old; do
-            [ $netdev == $check ] && break
-	done
-
-	if [ $netdev != $check ]; then
-	    echo $netdev
-	    break
-	fi
-    done
-}
-
 function check {
     local code=$1
     local str=$2
@@ -65,5 +48,6 @@ function make_netdev {
     fi
 
     echo $NSIM_ID > /sys/bus/netdevsim/new_device
-    echo `get_netdev_name old_netdevs`
+    # get new device name
+    ls /sys/bus/netdevsim/devices/netdevsim${NSIM_ID}/net/
 }