CTAP_CONT_HEADER_LEN
if (d->tx_len - CTAP_CONT_HEADER_LEN > sizeof(fp->body.cont.data))
count = MIN(count, d->tx_len - CTAP_CONT_HEADER_LEN);
uint8_t data[CTAP_MAX_REPORT_LEN - CTAP_CONT_HEADER_LEN];
d->rx_len <= CTAP_CONT_HEADER_LEN)
cont_data_len = d->rx_len - CTAP_CONT_HEADER_LEN;