gsm0808: Fix encoding of the SAPI_N_REJECT BSSMAP message.

See TS 08.08 section 3.2.1.34 SAPI "n" REJECT:
1) DLCI is a TV element, not V.
2) Cause is a TLV element and we have a special function to encode it.

Change-Id: I033afe556c06427d06ac55c4f78854a45e41aae6
diff --git a/tests/gsm0808/gsm0808_test.c b/tests/gsm0808/gsm0808_test.c
index 2389218..ec24914 100644
--- a/tests/gsm0808/gsm0808_test.c
+++ b/tests/gsm0808/gsm0808_test.c
@@ -370,7 +370,7 @@
 
 static void test_create_sapi_reject()
 {
-	static const uint8_t res[] = { 0x00, 0x03, 0x25, 0x03, 0x25 };
+	static const uint8_t res[] = { 0x00, 0x06, 0x25, 0x18, 0x03, 0x04, 0x01, 0x25 };
 	struct msgb *msg;
 
 	printf("Testing creating SAPI Reject\n");