selftests/bpf: Add test result messages for test_task_storage_map_stress_lookup

Add test result message when test_task_storage_map_stress_lookup()
succeeds or is skipped. The test case can be skipped due to the choose
of preemption model in kernel config, so export skips in test_maps.c and
increase it when needed.

The following is the output of test_maps when the test case succeeds or
is skipped:

test_task_storage_map_stress_lookup:PASS
test_maps: OK, 0 SKIPPED

test_task_storage_map_stress_lookup SKIP (no CONFIG_PREEMPT)
test_maps: OK, 1 SKIPPED

Fixes: 73b97bc78b32 ("selftests/bpf: Test concurrent updates on bpf_task_storage_busy")
Signed-off-by: Hou Tao <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin KaFai Lau <[e-mail]>

tools/testing/selftests/bpf/map_tests/task_storage_map.c

···
 	CHECK(err, "open_and_load", "error %d\n", err);
 
 	/* Only for a fully preemptible kernel */
-	if (!skel->kconfig->CONFIG_PREEMPT)
+	if (!skel->kconfig->CONFIG_PREEMPT) {
+		printf("%s SKIP (no CONFIG_PREEMPT)\n", __func__);
+		skips++;
 		return;
+	}
 
 	/* Save the old affinity setting */
 	sched_getaffinity(getpid(), sizeof(old), &old);
···
 	read_bpf_task_storage_busy__destroy(skel);
 	/* Restore affinity setting */
 	sched_setaffinity(getpid(), sizeof(old), &old);
+	printf("%s:PASS\n", __func__);
 }

tools/testing/selftests/bpf/test_maps.c

···
 #define ENOTSUPP 524
 #endif
 
-static int skips;
+int skips;
 
 static struct bpf_map_create_opts map_opts = { .sz = sizeof(map_opts) };
 

tools/testing/selftests/bpf/test_maps.h

···
 	}								\
 })
 
+extern int skips;
+
 #endif