RUM_N_TRANSFER
static const struct usb_config rum_config[RUM_N_TRANSFER] = {
sc->sc_xfer, rum_config, RUM_N_TRANSFER, sc, &sc->sc_mtx);
usbd_transfer_unsetup(sc->sc_xfer, RUM_N_TRANSFER);
struct usb_xfer *sc_xfer[RUM_N_TRANSFER];