FlowEntry must not be modified outside store.

- Remove set method from FlowEntry
- Storing last seen timestamp for FlowEntry eviction locally on FlowManager.
  FlowEntry eviction based on packet counter will take longer time to timeout
  after master Node change.

Change-Id: I7134d698dd5b9bf7cca379c5ba7c4fbcc2e3d5f3
diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java b/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
index 7513894..905469f 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
@@ -6,7 +6,8 @@
 import org.onlab.onos.net.DeviceId;
 import org.slf4j.Logger;
 
-public class DefaultFlowEntry extends DefaultFlowRule implements FlowEntry {
+public class DefaultFlowEntry extends DefaultFlowRule
+    implements FlowEntry, StoredFlowEntry {
 
     private static final Logger log = getLogger(DefaultFlowEntry.class);