Remove listeners before shutting down the executors

Change-Id: I1496ec06a839bb893e35a2e6d322d9eed33f45f2
diff --git a/apps/portloadbalancer/src/main/java/org/onosproject/portloadbalancer/app/PortLoadBalancerManager.java b/apps/portloadbalancer/src/main/java/org/onosproject/portloadbalancer/app/PortLoadBalancerManager.java
index ed59699..b040147 100644
--- a/apps/portloadbalancer/src/main/java/org/onosproject/portloadbalancer/app/PortLoadBalancerManager.java
+++ b/apps/portloadbalancer/src/main/java/org/onosproject/portloadbalancer/app/PortLoadBalancerManager.java
@@ -171,6 +171,8 @@
         portLoadBalancerStore.removeListener(portLoadBalancerStoreListener);
         portLoadBalancerNextStore.removeListener(portLoadBalancerNextStoreListener);
 
+        deviceService.removeListener(deviceListener);
+
         portLoadBalancerEventExecutor.shutdown();
         portLoadBalancerProvExecutor.shutdown();
         deviceEventExecutor.shutdown();