Make the default value of rtcp-mux policy to required.

webrtc/api/android/java/src/org/webrtc/PeerConnection.java

 /*
  *  Copyright 2013 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.
  */
 
@@ skipping 128 matching lines @@
     public int iceBackupCandidatePairPingInterval;
     public KeyType keyType;
     public ContinualGatheringPolicy continualGatheringPolicy;
     public int iceCandidatePoolSize;
     public boolean pruneTurnPorts;
     public boolean presumeWritableWhenFullyRelayed;
 
     public RTCConfiguration(List<IceServer> iceServers) {
       iceTransportsType = IceTransportsType.ALL;
       bundlePolicy = BundlePolicy.BALANCED;
-      rtcpMuxPolicy = RtcpMuxPolicy.NEGOTIATE;
+      rtcpMuxPolicy = RtcpMuxPolicy.REQUIRE;
       tcpCandidatePolicy = TcpCandidatePolicy.ENABLED;
       candidateNetworkPolicy = candidateNetworkPolicy.ALL;
       this.iceServers = iceServers;
       audioJitterBufferMaxPackets = 50;
       audioJitterBufferFastAccelerate = false;
       iceConnectionReceivingTimeout = -1;
       iceBackupCandidatePairPingInterval = -1;
       keyType = KeyType.ECDSA;
       continualGatheringPolicy = ContinualGatheringPolicy.GATHER_ONCE;
       iceCandidatePoolSize = 0;
@@ skipping 147 matching lines @@
   private native RtpSender nativeCreateSender(String kind, String stream_id);
 
   private native List<RtpSender> nativeGetSenders();
 
   private native List<RtpReceiver> nativeGetReceivers();
 
   private native boolean nativeStartRtcEventLog(int file_descriptor, int max_size_bytes);
 
   private native void nativeStopRtcEventLog();
 }