sample: bpf: syscall_tp_user: Print result of verify_map

At the end of the test, we already print out
    prog <prog number>: map ids <...> <...>
Value is the number read from kernel through bpf map, further print out
    verify map:<map id> val:<...>
will help users to understand the program runs successfully.

Signed-off-by: Song Chen <chensong_2000@189.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1648889828-12417-1-git-send-email-chensong_2000@189.cn

samples/bpf/syscall_tp_user.c

@@ -36,6 +36,9 @@ static void verify_map(int map_id)
 		fprintf(stderr, "failed: map #%d returns value 0\n", map_id);
 		return;
 	}
+
+	printf("verify map:%d val: %d\n", map_id, val);
+
 	val = 0;
 	if (bpf_map_update_elem(map_id, &key, &val, BPF_ANY) != 0) {
 		fprintf(stderr, "map_update failed: %s\n", strerror(errno));