HPCC-18080 Roxie PING message should report units

Saves me having to scan the source any time anyone asks me what it means.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>

roxie/ccd/ccdqueue.cpp

@@ -2846,7 +2846,7 @@ public:
                 if (!pingsReceived && roxieMulticastEnabled)
                     DBGLOG("PING: NO replies received! Please check multicast settings, and that your network supports multicast.");
                 else if (traceLevel)
-                    DBGLOG("PING: %d replies received, average delay %d", pingsReceived, pingsReceived ? pingsElapsed / pingsReceived : 0);
+                    DBGLOG("PING: %d replies received, average delay %uus", pingsReceived, pingsReceived ? pingsElapsed / pingsReceived : 0);
                 pingsReceived = 0;
                 pingsElapsed = 0;
                 sendPing(ROXIE_HIGH_PRIORITY);  // MORE - we could think about alternating the priority or sending pings on high and low at the same time...