mme: Implement missing UE attach steps

Related: OS#6294
Change-Id: Ib4a69aef40bf9dd17d640f650e459668f8415aaa
diff --git a/library/GTPv2_Templates.ttcn b/library/GTPv2_Templates.ttcn
index 1ccbcb8..c09bca8 100644
--- a/library/GTPv2_Templates.ttcn
+++ b/library/GTPv2_Templates.ttcn
@@ -1040,6 +1040,65 @@
 		privateExtension := omit
 	}});
 
+template (present) PDU_GTPCv2
+tr_GTP2C_ModifyBearerReq(template (present) OCT4 d_teid := ?,
+			  template (present) OCT3 seq := ?) :=
+tr_PDU_GTP2C(d_teid, seq, {
+	modifyBearerRequest := {
+		mEI := *,
+		userLocationInfo := *,
+		servingNetwork := *,
+		rAT_Type := *,
+		indicationFlags := *,
+		fullyQualifiedTEID := *,
+		ambr := *,
+		delayDownlinkPacketNotificationReq := *,
+		bearerContextGrouped := *,
+		recovery := *,
+		uE_TimeZone := *,
+		csid := *,
+		user_CSG_Information := *,
+		iP_Addr := *,
+		portNumber := *,
+		lDN := *,
+		//maxMBR_APN_AMBR := *,
+		cNOperatorSelectionEntity := *,
+		presenceReportingAreaInformation := *,
+		overloadControlInformationGrouped := *,
+		servingPLMNRateControl := *,
+		counter := *,
+		privateExtension := *
+	}});
+
+template (value) PDU_GTPCv2
+ts_GTP2C_ModifyBearerResp(template (value) OCT4 d_teid,
+			  template (value) OCT3 seq,
+			  template (value) GTP2C_Cause cause,
+			  template (value) uint4_t bearer_id,
+			  template (omit) BearerContextGrouped_List bearerContextGrouped := omit) :=
+ts_PDU_GTP2C(d_teid, seq, '23'O, {
+	modifyBearerResponse := {
+		cause := ts_GTP2C_Cause(cause, '0'B),
+		mSISDN := omit,
+		linkedEPS_Bearer_ID := ts_GTP2C_EpsBearerId(bearer_id),
+		aPN_Restriction := omit,
+		protocolConfigOptions := omit,
+		bearerContextGrouped := bearerContextGrouped,
+		changeReportingAction := omit,
+		cSG_InformationReportingAction := omit,
+		heNBInformationReporting := omit,
+		chargingGatewayName := omit,
+		chargingGatewayAddress := omit,
+		csid := omit,
+		recovery := omit,
+		lDN := omit,
+		indicationFlags := omit,
+		presenceReportingAreaAction := omit,
+		loadControlInformationGrouped := omit,
+		overloadControlInformationGrouped := omit,
+		pDNConnectionChargingID := omit,
+		privateExtension := omit
+	}});
 
 template (value) PDU_GTPCv2
 ts_GTP2C_DeleteBearerReq(template (value) OCT4 d_teid,