Bugfix/sync issue (#108)

* Add IE, universal time, in the configuration update command message:
* Add TimeZone field in the AMFContext.

* Fix bug: the format of time zone is wrong

* Modify BuildConfigurationUpdateCommand

* Update go module

* Fix bug: There is a synchronization issue between step 5 and step 11 during the procedure of UE Requested PDU Session Establishment.

internal/gmm/handler.go

@@ -265,6 +265,9 @@ func CreatePDUSession(ulNasTransport *nasMessage.ULNASTransport,
 		gmm_message.SendDLNASTransport(ue.RanUe[anType], nasMessage.PayloadContainerTypeN1SMInfo,
 			smMessage, pduSessionID, cause, nil, 0)
 	} else {
+		ue.Lock.Lock()
+		defer ue.Lock.Unlock()
+
 		_, smContextRef, errResponse, problemDetail, err := consumer.SendCreateSmContextRequest(
 			ue, newSmContext, nil, smMessage)
 		if err != nil {