Listener enhancement to allow separation of filtering from processing.

Change-Id: I79b4d7e663ea8347f8cc015dc7f4de842b06557b
diff --git a/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java b/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
index c84fb68..e6af201 100644
--- a/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
+++ b/core/api/src/main/java/org/onosproject/event/ListenerRegistry.java
@@ -71,7 +71,9 @@
             try {
                 lastListener = listener;
                 lastStart = System.currentTimeMillis();
-                listener.event(event);
+                if (listener.isRelevant(event)) {
+                    listener.event(event);
+                }
                 lastStart = 0;
             } catch (Exception error) {
                 reportProblem(event, error);