getprevious should fetch the previous stats from the store

Change-Id: Ia954e128d2503e4e787d496385c456ff249fc139
diff --git a/core/net/src/main/java/org/onlab/onos/net/statistic/impl/StatisticManager.java b/core/net/src/main/java/org/onlab/onos/net/statistic/impl/StatisticManager.java
index f1ac9b16..7ba03b8 100644
--- a/core/net/src/main/java/org/onlab/onos/net/statistic/impl/StatisticManager.java
+++ b/core/net/src/main/java/org/onlab/onos/net/statistic/impl/StatisticManager.java
@@ -208,7 +208,7 @@
      * @return set of flow entries
      */
     private Set<FlowEntry> getPreviousStatistic(ConnectPoint connectPoint) {
-        Set<FlowEntry> stats = statisticStore.getCurrentStatistic(connectPoint);
+        Set<FlowEntry> stats = statisticStore.getPreviousStatistic(connectPoint);
         if (stats == null) {
             return Collections.emptySet();
         } else {