Osmocom_Gb_Types: Fix t_BVC_FC_BVC_ACK() TAG IE length

Change-Id: Ib9a09fea85110a4f0966c07d911e37234aa06391
diff --git a/library/Osmocom_Gb_Types.ttcn b/library/Osmocom_Gb_Types.ttcn
index 2afedcc..ba05f7d 100644
--- a/library/Osmocom_Gb_Types.ttcn
+++ b/library/Osmocom_Gb_Types.ttcn
@@ -1255,7 +1255,7 @@
 				iEI := '1E'O,
 				ext := '1'B,
 				lengthIndicator := {
-					length1 := 2
+					length1 := 1
 				},
 				unstructured_Value := tag
 			}