[ONOS-6806] Add getAvailableDeviceCount method to DeviceService

Change-Id: Ieda7e66c1a1d25aa92b55542ecfe59652dac3bc5
diff --git a/core/api/src/main/java/org/onosproject/net/device/DeviceServiceAdapter.java b/core/api/src/main/java/org/onosproject/net/device/DeviceServiceAdapter.java
index 9c6887c..146a93a 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DeviceServiceAdapter.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DeviceServiceAdapter.java
@@ -56,6 +56,11 @@
     }
 
     @Override
+    public int getAvailableDeviceCount() {
+        return 0;
+    }
+
+    @Override
     public Iterable<Device> getDevices() {
         return Collections.emptyList();
     }