drop CWS to 2 if reno fast re-transmit is hit

libraries/networking/src/udt/TCPVegasCC.cpp

@@ -108,6 +108,9 @@ bool TCPVegasCC::onACK(SequenceNumber ack, p_high_resolution_clock::time_point r
             _numACKSinceFastRetransmit = 0;
             _duplicateACKCount = 0;
 
+            // drop the congestion window size to 2 segments
+            _congestionWindowSize = 2;
+
             // return true so the caller knows we needed a fast re-transmit
             return true;
         }