As found in 6f2b39c1be6a8b9531264d92138dc2629d51cfa0, you can't just register a control callback by itself, you can only register them in the set config callback, (or, at least, _after_ set config has been done. This has been compile tested only for the extra examples that were found to have this failing pattern.
README
This example implements a USB bootloader for the Paparazzi project.
TODO: Move to examples/lisa-m?