selftests/ipc: Fix test failure seen after initial test run

After successfully running the IPC msgque test once, subsequent runs
result in a test failure:

  $ sudo ./run_kselftest.sh
  TAP version 13
  1..1
  # selftests: ipc: msgque
  # Failed to get stats for IPC queue with id 0
  # Failed to dump queue: -22
  # Bail out!
  # # Pass 0 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 0
  not ok 1 selftests: ipc: msgque # exit=1

The dump_queue() function loops through the possible message queue index
values using calls to msgctl(kern_id, MSG_STAT, ...) where kern_id
represents the index value. The first time the test is ran, the initial
index value of 0 is valid and the test is able to complete. The index
value of 0 is not valid in subsequent test runs and the loop attempts to
try index values of 1, 2, 3, and so on until a valid index value is
found that corresponds to the message queue created earlier in the test.

The msgctl() syscall returns -1 and sets errno to EINVAL when invalid
index values are used. The test failure is caused by incorrectly
comparing errno to -EINVAL when cycling through possible index values.

Fix invalid test failures on subsequent runs of the msgque test by
correctly comparing errno values to a non-negated EINVAL.

Fixes: 3a665531 ("selftests: IPC message queue copy feature test")
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ipc/msgque.c

@@ -137,7 +137,7 @@ int dump_queue(struct msgque_data *msgque)
 	for (kern_id = 0; kern_id < 256; kern_id++) {
 		ret = msgctl(kern_id, MSG_STAT, &ds);
 		if (ret < 0) {
-			if (errno == -EINVAL)
+			if (errno == EINVAL)
 				continue;
 			printf("Failed to get stats for IPC queue with id %d\n",
 					kern_id);