kernel: cover k_usleep() from user mode

No test was exercising the k_usleep() system call, run
the test case as a user thread to fix code coverage.

Signed-off-by: Andrew Boie <[email protected]>

Author: Andrew Boie

tests/kernel/sleep/prj.conf

@@ -2,3 +2,4 @@ CONFIG_IRQ_OFFLOAD=y
 CONFIG_ZTEST=y
 CONFIG_QEMU_TICKLESS_WORKAROUND=y
 CONFIG_SMP=n
+CONFIG_TEST_USERSPACE=y

tests/kernel/sleep/src/main.c

@@ -240,6 +240,6 @@ void test_main(void)
 {
 	ztest_test_suite(sleep,
 			 ztest_unit_test(test_sleep),
-			 ztest_unit_test(test_usleep));
+			 ztest_user_unit_test(test_usleep));
 	ztest_run_test_suite(sleep);
 }