Incorrect value for total data received with the VPN client

[Senyoret1]

Describe the bug
The /api/visors/{{pk}}/apps/vpn-client/connections API endpoint always returns 0 in the bandwidth_received field.

Environment information:

• OS: Linux

Steps to Reproduce
Steps to reproduce the behavior:

1. Use the a web browser to open {{SkywireManagerHost}}/#/vpn/{{NodePK}} . That will opend the VPN client app.
2. Select a valid VPN server and connect to it.
3. Use your internet connection and check in the UI the data transmission stats. It will should the upload/download speed and how many data has been uploaded, but the total downloaded data will always be 0.
4. Open the network tab of the web developer tools (in the browser) and check the calls to the /api/visors/{{pk}}/apps/vpn-client/connections API endpoint.

Actual behavior
The bandwidth_received field is always 0.

Expected behavior
The bandwidth_received field should contain the total amount of data received.

Additional context
Add any other context about the problem here.