do not do bandwidth estimation if total data downloaded is too small

bool HTTPBase::estimateBandwidth(int32_t *bandwidth_bps) {

    Mutex::Autolock autoLock(mLock);

    if (mNumBandwidthHistoryItems < 2) {

    // Do not do bandwidth estimation if we don't have enough samples, or

    // total bytes download are too small (<64K).

    // Bandwidth estimation from these samples can often shoot up and cause

    // unwanted bw adaption behaviors.

    if (mNumBandwidthHistoryItems < 2 || mTotalTransferBytes < 65536) {

        return false;

    }