Enable transport seq num extension on receive channel to suppress log warning.

webrtc/audio/audio_receive_stream.cc

Index: webrtc/audio/audio_receive_stream.cc
diff --git a/webrtc/audio/audio_receive_stream.cc b/webrtc/audio/audio_receive_stream.cc
index 64d008326d2691e068bd3d7c405dfd11a5fc9044..ebe271367b6a9ec4d7a2e56c71e00cfefdea0d5f 100644
--- a/webrtc/audio/audio_receive_stream.cc
+++ b/webrtc/audio/audio_receive_stream.cc
@@ -108,6 +108,7 @@ AudioReceiveStream::AudioReceiveStream(
           kRtpExtensionAbsoluteSendTime, extension.id);
       RTC_DCHECK(registered);
     } else if (extension.name == RtpExtension::kTransportSequenceNumber) {
+      channel_proxy_->EnableReceiveTransportSequenceNumber(extension.id);
       bool registered = rtp_header_parser_->RegisterRtpHeaderExtension(
           kRtpExtensionTransportSequenceNumber, extension.id);
       RTC_DCHECK(registered);