Add assignment operator to AudioEncoderRuntimeConfig

webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_config.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/modules/audio_coding/audio_network_adaptor/include/audio_network_adaptor_config.h"
 
 namespace webrtc {
 
 AudioEncoderRuntimeConfig::AudioEncoderRuntimeConfig() = default;
 
 AudioEncoderRuntimeConfig::~AudioEncoderRuntimeConfig() = default;
 
 AudioEncoderRuntimeConfig::AudioEncoderRuntimeConfig(
     const AudioEncoderRuntimeConfig& other) = default;
 
+AudioEncoderRuntimeConfig& AudioEncoderRuntimeConfig::operator=(
+    const AudioEncoderRuntimeConfig& other) = default;
+
 }  // namespace webrtc