Reseting lastStart timestamp on listener ejection and sink notification.

Change-Id: Id13c8517fb4eca84a34ead168055328c236d090b
diff --git a/core/net/src/main/java/org/onosproject/event/impl/CoreEventDispatcher.java b/core/net/src/main/java/org/onosproject/event/impl/CoreEventDispatcher.java
index 6d97460..2c9d9aa 100644
--- a/core/net/src/main/java/org/onosproject/event/impl/CoreEventDispatcher.java
+++ b/core/net/src/main/java/org/onosproject/event/impl/CoreEventDispatcher.java
@@ -155,6 +155,7 @@
         public void run() {
             long delta = System.currentTimeMillis() - lastStart;
             if (lastStart > 0 && delta > maxProcessMillis) {
+                lastStart = 0;
                 log.error("Event sink {} exceeded execution time limit: {} ms",
                           lastSink.getClass().getName(), delta);