Add task exclusion between FlowHandler and StatsCollector

If Statscollector and flow-handler run in parallel, when flow-handler is
modifying a flows, its possible that stats-collector tries to access
flow contents.

Add task exclusion between stats-collector and flow-handler for R2.2*.
In R3.0 and above these two task can run in parallel.

Change-Id: I9d4601f00b95890d7a3ffdfd0317d519be628d9c
Closes-Bug: #1554246

src/vnsw/agent/cmn/agent.cc

@@ -121,6 +121,7 @@ void Agent::SetAgentTaskPolicy() {
                      sizeof(db_exclude_list) / sizeof(char *));
 
     const char *flow_exclude_list[] = {
+        "Agent::StatsCollector",
         "io::ReaderTask",
         "Agent::PktFlowResponder",
         AGENT_INIT_TASKNAME