Added more event and listener interface definitions.
diff --git a/net/api/src/main/java/org/onlab/onos/net/link/LinkListener.java b/net/api/src/main/java/org/onlab/onos/net/link/LinkListener.java
new file mode 100644
index 0000000..03039db
--- /dev/null
+++ b/net/api/src/main/java/org/onlab/onos/net/link/LinkListener.java
@@ -0,0 +1,9 @@
+package org.onlab.onos.net.link;
+
+import org.onlab.onos.event.EventListener;
+
+/**
+ * Entity capable of receiving infrastructure link related events.
+ */
+public interface LinkListener extends EventListener<LinkEvent> {
+}