Add task exclusion between KSync and Flow processing

Flow setup and KSync task run in parallel, its possible that
flow_entry_map_ can be manipulated by both tasks in parallel. In this
case following scenario has happend,

     1. The flow found in flow_entry_map_ was deleted and DEL operation
     was sent to VRouter
     2. In "Allocate" routine, a flow-entry was found from
     flow_entry_map_.
     3. VRouter DEL processing complete and the flow-entry is freed
     4. The flow-entry found in (2) is freed and contents modified

Agent must have exclusion between KSync and Flow-setup till
parallel access between the two task is handled correctly.

Change-Id: Ib13a3c13222826accd398f8f45c8c105328c9070
Fixes-Bug: #1520797

src/vnsw/agent/cmn/agent.cc

@@ -173,6 +173,8 @@ void Agent::SetAgentTaskPolicy() {
         "Agent::StatsCollector",
         "db::DBTable",
         "Agent::PktFlowResponder",
+        kTaskFlowEvent,
+        kTaskFlowUpdate,
         AGENT_INIT_TASKNAME
     };
     SetTaskPolicyOne("Agent::KSync", ksync_exclude_list,