Lila: investigate clients reporting negative lag

[niklasf]

Jul 09 18:49:12 greco lila-websocket[7173]: [2019-07-09T18:49:12Z WARN  lila_websocket] protocol violation of client (Error("invalid value: integer `-9`, expected u32", line: 0, column: 0)): {"t":"p","l":-9}

[niklasf]

even: client reported negative lag: -1712

[niklasf]

related: #5294

[niklasf]

The last negative lag reported was yesterday, 2019-07-09T23:01:00Z. So it looks like https://github.com/ornicar/lila/pull/5294 fixed the issue.

cc @isaacl

[niklasf]

Or at least it has become much less frequent.

Just 3 exceptions logged in the last 2 days. Won't reopen, because I doubt anyone can be bothered, but here they are with user agents just in case:

[2019-07-11T09:28:43Z WARN  lila_websocket] negative lag: -1, user-agent: Some("Mozilla/5.0 (Windows NT 6.1; rv:67.0) Gecko/20100101 Firefox/67.0")
[2019-07-12T11:48:42Z WARN  lila_websocket] negative lag: -2, user-agent: Some("Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0")
[2019-07-12T11:49:14Z WARN  lila_websocket] negative lag: -3, user-agent: Some("Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0")