[ONOS-7573][Test successful] Mark online does not notify peers device subsystem

Change-Id: Ie347241325047cb65c836c849bec6aebad758820
diff --git a/core/api/src/main/java/org/onosproject/net/device/DeviceStore.java b/core/api/src/main/java/org/onosproject/net/device/DeviceStore.java
index 54bdf17..bd59838 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DeviceStore.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DeviceStore.java
@@ -93,9 +93,9 @@
      * Marks the device as available.
      *
      * @param deviceId device identifier
-     * @return true if availability change request was accepted and changed the state
+     * @return ready to send event describing what occurred; null if no change
      */
-    boolean markOnline(DeviceId deviceId);
+    DeviceEvent markOnline(DeviceId deviceId);
 
     /**
      * Updates the ports of the specified infrastructure device using the given
diff --git a/core/api/src/test/java/org/onosproject/net/device/DeviceStoreAdapter.java b/core/api/src/test/java/org/onosproject/net/device/DeviceStoreAdapter.java
index a5a2a90..63971b9 100644
--- a/core/api/src/test/java/org/onosproject/net/device/DeviceStoreAdapter.java
+++ b/core/api/src/test/java/org/onosproject/net/device/DeviceStoreAdapter.java
@@ -62,8 +62,8 @@
     }
 
     @Override
-    public boolean markOnline(DeviceId deviceId) {
-        return false;
+    public DeviceEvent markOnline(DeviceId deviceId) {
+        return null;
     }
 
     @Override