Use pong receive time rather than processing time

src/net.h

@@ -173,11 +173,14 @@ public:
     CDataStream vRecv;              // received message data
     unsigned int nDataPos;
 
+    int64_t nTime;                  // time (in microseconds) of message receipt.
+
     CNetMessage(int nTypeIn, int nVersionIn) : hdrbuf(nTypeIn, nVersionIn), vRecv(nTypeIn, nVersionIn) {
         hdrbuf.resize(24);
         in_data = false;
         nHdrPos = 0;
         nDataPos = 0;
+        nTime = 0;
     }
 
     bool complete() const