Fix/vpn stats

[ersonp]

Did you run make format && make check?
yes

Fixes #946

Changes:

• Fixed bandwidth

How to test this PR:

1. Start a vpn-server
2. Start a vpn-client and connect to the VPN server
3. Compare the stats in the UI with any networking tool like nload on wtun4 interface

[ersonp]

2022-05-10.17-52-58.mp4

The upload and download speeds are now almost the same as shown in the tool nload for the tun interface. We send the data in API in bytes which I suppose is converted to bits for the upload and download speed in the UI. We need to specify it a bit more clearly that the speed is in terms of bits as compared to the total that is in terms of bytes.

[
   {
      "is_alive":true,
      "latency":196,
      "upload_speed":691,
      "download_speed":561,
      "bandwidth_sent":624761,
      "bandwidth_received":665736,
      "error":"",
      "connection_duration":89
   }
]

The latency is still a bit inaccurate (working on it so see if anything more can be done) and shoots up whenever there is a big download (tested this with meter.net) and the ping spikes there too while a download is going on so the behaviour seems normal.

The ping to the server the vpn-server constantly gives a ping of 240 ms

[mrpalide]

I test it, and can confirm that Speed and Bandwidth are OK.

vpn-stat.mov

But ping is a few different from what showing in UI and results from teminal.