selftests: memory-hotplug: return Kselftest Skip code for skipped tests

When memory-hotplug test is skipped because of unmet dependencies and/or
unsupported configuration, it returns non-zero value hich is treated as a
fail by the Kselftest framework. This leads to false negative result even
when the test could not be run.

Change it to return kselftest skip code when a test gets skipped to
clearly report that the test could not be run.

Kselftest framework SKIP code is 4 and the framework prints appropriate
messages to indicate that the test is skipped.
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/memory-hotplug/mem-on-off-test.sh

@@ -3,30 +3,33 @@
 
 SYSFS=
 
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
 prerequisite()
 {
 	msg="skip all tests:"
 
 	if [ $UID != 0 ]; then
 		echo $msg must be run as root >&2
-		exit 0
+		exit $ksft_skip
 	fi
 
 	SYSFS=`mount -t sysfs | head -1 | awk '{ print $3 }'`
 
 	if [ ! -d "$SYSFS" ]; then
 		echo $msg sysfs is not mounted >&2
-		exit 0
+		exit $ksft_skip
 	fi
 
 	if ! ls $SYSFS/devices/system/memory/memory* > /dev/null 2>&1; then
 		echo $msg memory hotplug is not supported >&2
-		exit 0
+		exit $ksft_skip
 	fi
 
 	if ! grep -q 1 $SYSFS/devices/system/memory/memory*/removable; then
 		echo $msg no hot-pluggable memory >&2
-		exit 0
+		exit $ksft_skip
 	fi
 }