GSM_RR_Types: Add enc_RoutingAreaIdentification()

This allows us to encode a stand-alone RAID as needed in some places.

Change-Id: I28222304b2bac893b216c47e6dc002886fab6406
diff --git a/library/GSM_RR_Types.ttcn b/library/GSM_RR_Types.ttcn
index 26783f9..5958569 100644
--- a/library/GSM_RR_Types.ttcn
+++ b/library/GSM_RR_Types.ttcn
@@ -421,6 +421,9 @@
 		uint8_t				rac
 	} with { variant "" };
 
+	external function enc_RoutingAreaIdentification(RoutingAreaIdentification rai) return octetstring
+	with { extension "prototype(convert)" extension "encode(RAW)" }
+
 	/* 44.018 10.5.2.16 */
 	type record IaRestOctHL {
 		uint6_t		freq_par_len,