Fix 2 race conditions detected with TSan, one in CobraMetricsPublisher::push and another one in WebSocketTransport::sendData (that one was bad).

ixcobra/ixcobra/IXCobraConnection.cpp

@@ -462,6 +462,8 @@ namespace ix
         const Json::Value& msg,
         bool addToQueue)
     {
+        std::lock_guard<std::mutex> lock(_prePublishMutex);
+
         invokePublishTrackerCallback(true, false);
 
         CobraConnection::MsgId msgId = _id;

ixcobra/ixcobra/IXCobraConnection.h

@@ -181,6 +181,7 @@ namespace ix
         Json::Value _pdu;
         Json::FastWriter _jsonWriter;
         mutable std::mutex _jsonWriterMutex;
+        std::mutex _prePublishMutex;
 
         /// Traffic tracker callback
         static TrafficTrackerCallback _trafficTrackerCallback;