gsm0808_create_cipher_reject: Fix encoding of Cause IE

The Cause IE in the 08.08 CIPHER MODE REJECT is a normal TLV IE,
and not just a value.  Let's make sure we encode the cause value
properly.

Change-Id: I4f5b231edf6dcb0a9c2bbafb2a59f301f3b2402b
Closes: OS#2766
diff --git a/tests/gsm0808/gsm0808_test.c b/tests/gsm0808/gsm0808_test.c
index 28bd7f7..189d548 100644
--- a/tests/gsm0808/gsm0808_test.c
+++ b/tests/gsm0808/gsm0808_test.c
@@ -233,7 +233,7 @@
 
 static void test_create_cipher_reject()
 {
-	static const uint8_t res[] = { 0x00, 0x02, 0x59, 0x23 };
+	static const uint8_t res[] = { 0x00, 0x04, 0x59, 0x04, 0x01, 0x23 };
 	struct msgb *msg;
 
 	printf("Testing creating Cipher Reject\n");