Fix immediate fallback to long poll when websocket connection is lost

[peymor19]

When a browser client loses its web socket connection to the server, I noticed that it immediately falls back to long poll without respecting the longPollFallbackMs delay.

This causes all connected browser clients to fall back to long poll when restarting an Elixir server, instead of attempting to reconnect to a new web socket as expected.

I have added a failing test and a potential fix.

I am not sure that the implementation of the fix is the best so I would appreciate some insight on the issue before diving deeper into a better solution.

In this image you can see that I set the longPollFallbackMs to 5500 ms

This image shows the client immediately falling back to long poll instead of waiting the 5500ms for a web socket connection.

Thanks for your consideration!

[matheus1lva]

Im seing exactly the same thing, in my case even some next requests are being aborted because of that!