Support cipher mode reject with extended cause

* add function to generate cipher mode reject with extended (2-byte)
  Cause IE
* add function to get (extended) Cause value
* add corresponding (extended cause) test
* update existing (non-extended cause) test
* use enum as a parameter for existing non-extended version to make
  interface more unified

Change-Id: Id5509b94a18180a44f45300caaa02b843c166fa3
Related: OS#3187
diff --git a/tests/gsm0808/gsm0808_test.ok b/tests/gsm0808/gsm0808_test.ok
index 58bc509..a48cf1d 100644
--- a/tests/gsm0808/gsm0808_test.ok
+++ b/tests/gsm0808/gsm0808_test.ok
@@ -8,6 +8,7 @@
 Testing creating Chipher Mode Command
 Testing creating Cipher Complete
 Testing creating Cipher Reject
+Testing creating Cipher Reject (extended)
 Testing creating CM U
 Testing creating SAPI Reject
 Testing creating Assignment Request