tests/ussd: fix wrong GSM 04.80 payload length

Previously the same length value was used for both ussd_request
and interrogate_ss payloads, despite they are different.

Change-Id: I90ae7c51b75dcdb9d8ee042af23d127e6db8771d
diff --git a/tests/ussd/ussd_test.c b/tests/ussd/ussd_test.c
index bf6d731..8d88dbb 100644
--- a/tests/ussd/ussd_test.c
+++ b/tests/ussd/ussd_test.c
@@ -120,24 +120,28 @@
 int main(int argc, char **argv)
 {
 	struct ss_request req;
-	const int size = sizeof(ussd_request);
+	uint16_t size;
 	int i;
 	struct msgb *msg;
 
 	osmo_init_logging(&info);
 
 	memset(&req, 0, sizeof(req));
-	gsm0480_decode_ss_request((struct gsm48_hdr *) ussd_request, size, &req);
+	gsm0480_decode_ss_request((struct gsm48_hdr *) ussd_request,
+		sizeof(ussd_request), &req);
 	printf("Tested if it still works. Text was: %s\n", req.ussd_text);
 
 	memset(&req, 0, sizeof(req));
-	gsm0480_decode_ss_request((struct gsm48_hdr *) interrogate_ss, size, &req);
+	gsm0480_decode_ss_request((struct gsm48_hdr *) interrogate_ss,
+		sizeof(interrogate_ss), &req);
 	OSMO_ASSERT(strlen((char *) req.ussd_text) == 0);
 	OSMO_ASSERT(req.ss_code == 33);
 	printf("interrogateSS CFU text..'%s' code %d\n", req.ussd_text, req.ss_code);
 
 	printf("Testing parsing a USSD request and truncated versions\n");
 
+	size = sizeof(ussd_request);
+
 	for (i = size; i > sizeof(struct gsm48_hdr); --i) {
 		int rc = parse_ussd(&ussd_request[0], i);
 		printf("Result for len=%d is %d\n", i, rc);