Add short-cut path taking when the paremter type is equal to own type

Change-Id: Ifbc3ea11c901b1496adcc8d0a372c86cd27969e2
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
index b229308..4862606 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/UnifiedDiscreteResources.java
@@ -93,6 +93,15 @@
 
     @Override
     public DiscreteResources add(DiscreteResources other) {
+        if (other instanceof UnifiedDiscreteResources) {
+            UnifiedDiscreteResources cast = (UnifiedDiscreteResources) other;
+            return new UnifiedDiscreteResources(
+                    this.generics.add(cast.generics),
+                    this.encodables.add(cast.encodables));
+        } else if (other instanceof EmptyDiscreteResources) {
+            return this;
+        }
+
         return of(Sets.union(this.values(), other.values()));
     }