Merge "aaudio: fix mixer volume to match AudioTrack" into oc-dev

            std::lock_guard<std::mutex> lock(mLockStreams);

            for(AAudioServiceStreamShared *sharedStream : mRunningStreams) {

                FifoBuffer *fifo = sharedStream->getDataFifoBuffer();

                float volume = 0.5; // TODO get from system

                const float volume = 1.0f; // to match the perceived volume from AudioTrack

                bool underflowed = mMixer.mix(fifo, volume);

                underflowCount += underflowed ? 1 : 0;

                // TODO log underflows in each stream