These are the "main" worker threads (apart the ru_thread). If the
thread-pool stops, they might get stuck. E.g., in PUSCH channel
estimation, it uses a local response queue, and if the thread pool is
terminated, it seems that the L1_rx_thread can get stuck in there.
To limit these problems, attempt to stop these threads first; stop the
queue from which they read and make them terminate; then, stop the
thread pool.
Also, fix the termination of respPuschSymb queue.
Robert Schmidt
70b4611001