aggregate flow replies on io thread

Change-Id: I622290f213ee830cfab7e4bd4ad7a52f612b475e
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 2611a6d..d681524 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
@@ -355,7 +355,7 @@
 
         @Override
         public void pushFlowMetrics(DeviceId deviceId, Iterable<FlowEntry> flowEntries) {
-            List<FlowEntry> storedRules = Lists.newLinkedList(store.getFlowEntries(deviceId));
+            Set<FlowEntry> storedRules = Sets.newHashSet(store.getFlowEntries(deviceId));
 
             for (FlowEntry rule : flowEntries) {
                 if (storedRules.remove(rule)) {