Fixing null provider defects.

Change-Id: I3a4df1d5821e1961e1c70270a6be3642d0c3a60e
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/NullProviders.java b/providers/null/src/main/java/org/onosproject/provider/nil/NullProviders.java
index f6236c4..08be68a 100644
--- a/providers/null/src/main/java/org/onosproject/provider/nil/NullProviders.java
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/NullProviders.java
@@ -329,10 +329,10 @@
                        new DefaultServiceDirectory(),
                        deviceProviderService, hostProviderService,
                        linkProviderService);
-        simulator.setUpTopology();
         flowRuleProvider.start(flowRuleProviderService);
         packetProvider.start(packetRate, hostService, deviceService,
                              packetProviderService);
+        simulator.setUpTopology();
         topologyMutationDriver.start(mutationRate, linkService, deviceService,
                                      linkProviderService, deviceProviderService,
                                      simulator);