Support for walkera telemetry.

int CYRF_ReadDataPacket(int force, u8 dpbuffer[]) // "force" if not set RXOW EN in RX_CFG
{
    int ok = 0;
    u8 rx_state = CYRF_ReadRegister(CYRF_07_RX_IRQ_STATUS);
    if (rx_state & 0x01)    // RXE=1 bad data
        ok = -1;
    else if (rx_state & 0x02)    // receive complete
        // RXC=1, RXE=0 then 2nd check is required (debouncing)
        ok = (CYRF_ReadRegister(CYRF_07_RX_IRQ_STATUS) & 0x01) ? -1 : 1;

    if (ok == 1 || force) {
        CYRF_WriteRegister(CYRF_07_RX_IRQ_STATUS, 0x80);    // set RXOW before data read
        u8 length = CYRF_ReadRegister(CYRF_09_RX_COUNT);
        ReadRegisterMulti(CYRF_21_RX_BUFFER, dpbuffer, length);
        return (ok == 1) ? length : ok ;
    }
    return ok;
}

    CYRF_SetTxRxMode(TX_EN);
    CYRF_WriteRegister(CYRF_03_TX_CFG, 0x08 | Model.tx_power);

static void cyrf_set_bound_sop_code()
{
    /* crc == 0 isn't allowed, so use 1 if the math results in 0 */
    u8 crc = (cyrfmfg_id[0] + (cyrfmfg_id[1] >> 6) + cyrfmfg_id[2]);
    if(! crc)
        crc = 1;
    u8 sopidx = (0xff &((cyrfmfg_id[0] << 2) + cyrfmfg_id[1] + cyrfmfg_id[2])) % 10;
    CYRF_ConfigCRCSeed((crc << 8) + crc);
    CYRF_ConfigSOPCode(sopcodes[sopidx]);
}