Notify NetEqController during muted state.

During muted state NetEq shortcircuits a large part of the internals to
quickly return a buffer filled with zeros. It can be beneficial for the
controller to be aware that it is in muted state.

Bug: webrtc:11005
Change-Id: I5fe24b4a3704d953cbd68b5a24bbb7ef58b30be0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/186760
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Jakob Ivarsson <jakobi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32330}

modules/audio_coding/neteq/neteq_impl.cc

@@ -857,6 +857,7 @@ int NetEqImpl::GetAudioInternal(AudioFrame* audio_frame,
                   static_cast<uint32_t>(audio_frame->samples_per_channel_);
     audio_frame->num_channels_ = sync_buffer_->Channels();
     stats_->ExpandedNoiseSamples(output_size_samples_, false);
+    controller_->NotifyMutedState();
     *muted = true;
     return 0;
   }