handle congestion recovery in multi-threading mode

Currently when the talk queue is full the server run_one method skips the receivePacket() call and returns.

This has a bad impact on mechanisms using external sockets because they are not served.

I propose to handle the congestion recovery inside the multi-threading code itself:

• make the congestion recovery disabled at configuration time when multi-threading is enabled
• change the task queue (aka ThreadPool) by a ring