Simplify the code by using the constructor initializing a reference

Change-Id: I62335690903fe21cd3400e81e20833b4a1bb7b59
diff --git a/core/net/src/main/java/org/onosproject/net/flow/impl/FlowRuleManager.java b/core/net/src/main/java/org/onosproject/net/flow/impl/FlowRuleManager.java
index 7d1022c..3ca37cc 100644
--- a/core/net/src/main/java/org/onosproject/net/flow/impl/FlowRuleManager.java
+++ b/core/net/src/main/java/org/onosproject/net/flow/impl/FlowRuleManager.java
@@ -449,8 +449,7 @@
                 Multimap<DeviceId, FlowRuleBatchEntry> batches) {
             this.futures = futures;
             this.batches = batches;
-            state = new AtomicReference<>();
-            state.set(BatchState.STARTED);
+            this.state = new AtomicReference<>(BatchState.STARTED);
         }
 
         @Override