Simplify shm td iq channel implementation

Move the channel state management outside the channel implementation.
This simplifies the channel implementation but forces users of the
channel to manage it's state manually.

radio/vrtsim/vrtsim.c

@@ -368,10 +368,6 @@ static int vrtsim_connect(openair0_device *device)
                                                      vrtsim_state->peer_info.num_rx_antennas,
                                                      device->openair0_cfg[0].rx_num_channels);
     vrtsim_state->run_timing_thread = true;
-    while (!shm_td_iq_channel_is_connected(vrtsim_state->channel)) {
-      LOG_I(HW, "Waiting for client\n");
-      sleep(1);
-    }
     int ret = pthread_create(&vrtsim_state->timing_thread, NULL, vrtsim_timing_job, vrtsim_state);
     AssertFatal(ret == 0, "pthread_create() failed: errno: %d, %s\n", errno, strerror(errno));
   } else {