ot::Hdlc::Decoder::Decode() method

Feeds a block of data into the decoder. If during decoding, a full HDLC frame is successfully decoded or an error occurs, the `FrameHandler` callback is called. The decoded frame (or the partially decoded frame in case of an error) is available in `aFrameWritePointer` buffer from the constructor. The `Decoder` user (if required) must update/reset the write pointer from this callback for the next frame to be decoded.