Sent & Received bytes should be 0 if Interface is not defined

According to TR181 standard, the following parameters can only be accurately calculated if the Interface parameter is specified:

• Device.IP.Diagnostics.DownloadDiagnostics.TotalBytesSent
• Device.IP.Diagnostics.DownloadDiagnostics.TotalBytesReceived
• Device.IP.Diagnostics.UploadDiagnostics.TotalBytesSent
• Device.IP.Diagnostics.UploadDiagnostics.TotalBytesReceived

References:

• https://cwmp-data-models.broadband-forum.org/tr-181-2-18-1-cwmp.html#D.Device:2.Device.IP.Diagnostics.DownloadDiagnostics.TotalBytesSent
• https://cwmp-data-models.broadband-forum.org/tr-181-2-18-1-cwmp.html#D.Device:2.Device.IP.Diagnostics.DownloadDiagnostics.TotalBytesReceived
• https://cwmp-data-models.broadband-forum.org/tr-181-2-18-1-cwmp.html#D.Device:2.Device.IP.Diagnostics.UploadDiagnostics.TotalBytesSent
• https://cwmp-data-models.broadband-forum.org/tr-181-2-18-1-cwmp.html#D.Device:2.Device.IP.Diagnostics.UploadDiagnostics.TotalBytesReceived