selftests: net: change fprintf format specifiers

`cur64`, `start64` and `ts_delta` are int64_t. Change format
specifiers in fprintf from `"%lu"` to `"%" PRId64` to adapt
to 32-bit and 64-bit systems.
Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Link: https://lore.kernel.org/r/20220319073730.5235-1-guozhengkui@vivo.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/txtimestamp.c

@@ -161,7 +161,7 @@ static void validate_timestamp(struct timespec *cur, int min_delay)
 	max_delay = min_delay + cfg_delay_tolerance_usec;
 
 	if (cur64 < start64 + min_delay || cur64 > start64 + max_delay) {
-		fprintf(stderr, "ERROR: %lu us expected between %d and %d\n",
+		fprintf(stderr, "ERROR: %" PRId64 " us expected between %d and %d\n",
 				cur64 - start64, min_delay, max_delay);
 		test_failed = true;
 	}
@@ -170,9 +170,9 @@ static void validate_timestamp(struct timespec *cur, int min_delay)
 static void __print_ts_delta_formatted(int64_t ts_delta)
 {
 	if (cfg_print_nsec)
-		fprintf(stderr, "%lu ns", ts_delta);
+		fprintf(stderr, "%" PRId64 " ns", ts_delta);
 	else
-		fprintf(stderr, "%lu us", ts_delta / NSEC_PER_USEC);
+		fprintf(stderr, "%" PRId64 " us", ts_delta / NSEC_PER_USEC);
 }
 
 static void __print_timestamp(const char *name, struct timespec *cur,