only process cp tail if in the right spot

libraries/networking/src/udt/Connection.cpp

@@ -746,6 +746,7 @@ void Connection::processTimeoutNAK(std::unique_ptr<ControlPacket> controlPacket)
 }
 
 void Connection::processProbeTail(std::unique_ptr<ControlPacket> controlPacket) {
+    if (((uint32_t) _lastReceivedSequenceNumber & 0xF) == 0) {
         // this is the second packet in a probe set so we can estimate bandwidth
         // the sender sent this to us in lieu of sending new data (because they didn't have any)
         
@@ -758,6 +759,7 @@ void Connection::processProbeTail(std::unique_ptr<ControlPacket> controlPacket)
         // mark that we processed a control packet for the second in the pair and we should not mark
         // the next data packet received
         _receivedControlProbeTail = true;
+    }
 }
 
 void Connection::resetReceiveState() {