hci: Stop the thread before hci_close()

  alarm_free(startup_timer);

  startup_timer = NULL;

  hci_close();

  // Stop the thread to prevent Send() calls.

  if (thread) {

    thread_stop(thread);

    thread_join(thread);

  }

  // Close HCI to prevent callbacks.

  hci_close();

  fixed_queue_free(command_queue, osi_free);

  command_queue = NULL;

  fixed_queue_free(packet_queue, buffer_allocator->free);