L3_Templates: tr_GMM_DET_REQ_MT: use * instead of omit for `cause`

The omit force this field to be not present, while a * allows to be present or not.
As user of this tr I would expect to ignore this field rather than an explicit omit.

Change-Id: Iae91f752789273934a6382bdd474594c3c50bbe9
diff --git a/library/L3_Templates.ttcn b/library/L3_Templates.ttcn
index b346da6..d0f1406 100644
--- a/library/L3_Templates.ttcn
+++ b/library/L3_Templates.ttcn
@@ -2191,7 +2191,7 @@
 template PDU_L3_SGSN_MS tr_GMM_DET_REQ_MT(
 		template BIT3 dtt := *,
 		template BIT3 forceToStandby := ?,
-		template OCT1 cause := omit) := {
+		template OCT1 cause := *) := {
 	discriminator := '1000'B,
 	tiOrSkip := {
 		skipIndicator := '0000'B