Update TRexClient.java

only set core mask on start_traffic when it is bigger than zero

Author: Emil-Gustafsson

src/main/java/com/cisco/trex/stateless/TRexClient.java

@@ -330,7 +330,9 @@ public void startTraffic(
       Map<String, Object> mul,
       int coreMask) {
     Map<String, Object> payload = createPayload(portIndex, profileId);
-    payload.put("core_mask", coreMask);
+    if (coreMask > 0) {
+      payload.put("core_mask", coreMask);
+    }
     payload.put("mul", mul);
     payload.put("duration", duration);
     payload.put("force", force);