Fix traffic statistics in TwoPartyTupleGenerator (#160)

Summary:
Pull Request resolved: #160

gorel raised the issue in D34779616 that the number of bytes sent/received was roughly the same for publisher and partner, whereas they should just be inverted.

This should fix it.

Reviewed By: chualynn

Differential Revision: D35199261

fbshipit-source-id: 9e9a4a22122812ce107a20b9b45e575a789c0dd7

fbpcf/engine/tuple_generator/TwoPartyTupleGenerator.cpp

@@ -129,7 +129,7 @@ std::pair<uint64_t, uint64_t> TwoPartyTupleGenerator::getTrafficStatistics()
   auto senderStats = senderRcot_->getTrafficStatistics();
   auto receiverStats = receiverRcot_->getTrafficStatistics();
   rst.first += senderStats.first + receiverStats.first;
-  rst.second += senderStats.first + receiverStats.second;
+  rst.second += senderStats.second + receiverStats.second;
 
   return rst;
 }