Issue: Multiple subscription sent for same routing instance from agent.

Agent uses two fields stored in DB state of vrf entry to identify if
subscription needs to be send or not. One is the subscription status and
other is force_change. Forced update is done when channel flaps. On flaps
subscription is set to true however it needs to be sent again so the walker
marks forced change to be true and issues a notify.
After doing notify this forced change field is not reset to false.
Because of that any update in VRF results in resending the subscription to CN.

Solution: Reset the force change field after request is processed.

Change-Id: Ib95720fcfe92200f1012762ff68c33d5d376d3bb
Closes-bug: #1429254

src/vnsw/agent/controller/controller_vrf_export.cc

@@ -90,6 +90,7 @@ void VrfExport::Notify(AgentXmppChannel *bgp_xmpp_peer,
                                            fabric_vrf_name()) != 0) {
                     bgp_peer->route_walker()->StartRouteWalk(vrf);
                 }
+                state->force_chg_ = false;
             }
             return;
         }

src/vnsw/agent/test/test_xmppcs_bcast.cc

@@ -108,6 +108,19 @@ class ControlNodeMockBgpXmppPeer {
     }
 
     void ReceiveUpdate(const XmppStanza::XmppMessage *msg) {
+        if (msg->type == XmppStanza::IQ_STANZA) {
+            const XmppStanza::XmppMessageIq *iq =
+                static_cast<const XmppStanza::XmppMessageIq *>(msg);
+            if (iq->iq_type.compare("set") == 0) {
+                if (iq->action.compare("subscribe") == 0) {
+                    assert(vrf_subscription_.find(iq->node) ==
+                           vrf_subscription_.end());
+                    vrf_subscription_[iq->node] = true;
+                } else if (iq->action.compare("unsubscribe") == 0) {
+                    vrf_subscription_.erase(iq->node);
+                }
+            }
+        }
         rx_count_++;
     }
 
@@ -128,6 +141,7 @@ class ControlNodeMockBgpXmppPeer {
 private:
     XmppChannel *channel_;
     size_t rx_count_;
+    std::map<string, bool> vrf_subscription_;
 };
 
 
@@ -531,7 +545,7 @@ class AgentXmppUnitTest : public ::testing::Test {
 	//Verify mpls table
 	WAIT_FOR(1000, 1000, (Agent::GetInstance()->mpls_table()->
                           FindMplsLabel(alloc_label+ 1) == NULL));
-	WAIT_FOR(1000, 1000, (Agent::GetInstance()->mpls_table()->Size() == 5));
+	WAIT_FOR(1000, 1000, (Agent::GetInstance()->mpls_table()->Size() == 7));
     }
 
     void XmppSubnetTearDown() {