Adding a namespace comment

This was pointed out in https://codereview.webrtc.org/1772583002/.

BUG=webrtc:5607 NOTRY=true
TBR=kwiberg@webrtc.org

Review URL: https://codereview.webrtc.org/1774933002

Cr-Commit-Position: refs/heads/master@{#11908}

webrtc/modules/audio_coding/neteq/neteq_impl.cc

@@ -189,7 +189,7 @@ void SetAudioFrameActivityAndType(bool vad_enabled,
     audio_frame->vad_activity_ = AudioFrame::kVadUnknown;
   }
 }
-}
+}  // namespace
 
 int NetEqImpl::GetAudio(AudioFrame* audio_frame) {
   TRACE_EVENT0("webrtc", "NetEqImpl::GetAudio");