Added STC shutdown scenario.

Change-Id: I48b882c872f69fdd84fe2fd057163e68ffb58012
diff --git a/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java b/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
index 56d41ff..586365a 100644
--- a/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
+++ b/providers/openflow/device/src/main/java/org/onosproject/provider/of/device/impl/OpenFlowDeviceProvider.java
@@ -141,8 +141,8 @@
     public void deactivate() {
         providerRegistry.unregister(this);
         controller.removeListener(listener);
+        collectors.values().forEach(PortStatsCollector::stop);
         providerService = null;
-
         LOG.info("Stopped");
     }
 
@@ -165,6 +165,7 @@
         if (sw == null || !sw.isConnected()) {
             LOG.error("Failed to probe device {} on sw={}", deviceId, sw);
             providerService.deviceDisconnected(deviceId);
+            return;
         } else {
             LOG.trace("Confirmed device {} connection", deviceId);
         }