Enable periodic bitrate probing when application limited for audio BWE.

webrtc/audio/audio_send_stream.cc

Index: webrtc/audio/audio_send_stream.cc
diff --git a/webrtc/audio/audio_send_stream.cc b/webrtc/audio/audio_send_stream.cc
index cb4c1b041c81bc44f16ce4d3df6d8477fb1bdb8c..d8bc84858a6a3e33936a89dd1dfa6c6c173d68b9 100644
--- a/webrtc/audio/audio_send_stream.cc
+++ b/webrtc/audio/audio_send_stream.cc
@@ -82,6 +82,7 @@ AudioSendStream::AudioSendStream(
       channel_proxy_->SetSendAudioLevelIndicationStatus(true, extension.id);
     } else if (extension.uri == RtpExtension::kTransportSequenceNumberUri) {
       channel_proxy_->EnableSendTransportSequenceNumber(extension.id);
+      congestion_controller->EnablePeriodicAlrProbing(true);
     } else {
       RTC_NOTREACHED() << "Registering unsupported RTP extension.";
     }