[ONOS-6324] Add getOrDefault method to ConsistentMap.

Change-Id: Ice7ad6260c6eb8076320ef469874c0c4ceeadc19
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DelegatingAsyncConsistentTreeMap.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DelegatingAsyncConsistentTreeMap.java
index 31d5f8e..48c0b85 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DelegatingAsyncConsistentTreeMap.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/DelegatingAsyncConsistentTreeMap.java
@@ -160,6 +160,11 @@
     }
 
     @Override
+    public CompletableFuture<Versioned<V>> getOrDefault(String key, V defaultValue) {
+        return delegateMap.getOrDefault(key, defaultValue);
+    }
+
+    @Override
     public CompletableFuture<Versioned<V>> computeIf(
             String key,
             Predicate<? super V> condition,