Update Bdx TransferFacilitator to allow for cancelling the PollTimerHandler

[hubTab]

Problem

In the BdxOtaSender::TransferFacilitator.cpp there is no way currently to cancel the PollTimerHandler, as needed, when receiving an kAckEOFReceived . The problem is that calling chip::DeviceLayer::SystemLayer().CancelTimer(PollTimerHandler, this); upon receiving kAckEOFReceived, it does not cancel the PollTimerHandler, as TransferFacilitator::PollForOutput() re-registers it.

Proposed Solution

While the BdxOtaSender was provided as en example, that terminates when upon completing the Bdx transfer, the TransferFacilitator.cpp needs to allow cancelling the PollTimerHandler.

To accomplish it, adding a mStopPolling flag in TransferFacilitator::PollForOutput() allowed for cancelling the PollTimerHandler.

Testing

Using a full OTA Download using M5Stack, enabled with OTA Requestor.