Merge "adb: fix deadlock."

static int hotplug_callback(libusb_context*, libusb_device* device, libusb_hotplug_event event,

                            void*) {

    // We're called with the libusb lock taken. Call these on the main thread outside of this

    // function so that the usb_handle mutex is always taken before the libusb mutex.

    fdevent_run_on_main_thread([device, event]() {

        if (event == LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED) {

            device_connected(device);

        } else if (event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT) {

            device_disconnected(device);

        }

    });

    return 0;

}