TeaVM proxy drops websocket connection

[Ihromant]

Hi I tried to perform obvious fix for websocket which is dropped after 300 seconds 287333b
But seems that it didn't help. Steps to reproduce the issue:

1. Create simple websocket application with Jetty.
2. Perform disabling of session drop on server side.

@OnWebSocketOpen
    public void onWebSocketConnect(Session session) {
        this.session = session; // save session
        session.setIdleTimeout(Duration.ZERO); // disable inactive session drop
    }

3. Run jetty on localhost:8080. Launch TeaVM proxy for 9090. Open websocket http://localhost:9090/websocket session in JS. Wait 300 seconds. Session will be closed. When open same websocket on localhost:8080 it is not closed.