Fix the EVPN orch may access invalid address

There is an private pointer in the EVPN orch which is used save the local
vtep. But the local vtep is add/removed in the vxlan tunnel orch, the
vxlan tunnel orch did not notify EVPN orch when remove the vtep and cause
EVPN orch may access invalid address

orchagent/vxlanorch.cpp

@@ -1391,6 +1391,7 @@ bool VxlanTunnelOrch::delOperation(const Request& request)
     SWSS_LOG_ENTER();
 
     const auto& tunnel_name = request.getKeyString(0);
+    EvpnNvoOrch* evpn_orch = gDirectory.get<EvpnNvoOrch*>();
 
     if (!isTunnelExists(tunnel_name))
     {
@@ -1405,6 +1406,11 @@ bool VxlanTunnelOrch::delOperation(const Request& request)
         return false;
     }
 
+    if (vtep_ptr == evpn_orch->getEVPNVtep())
+    {
+	evpn_orch->delEVPNVtep();
+    }
+
     vxlan_tunnel_table_.erase(tunnel_name);
 
     SWSS_LOG_NOTICE("Vxlan tunnel '%s' was removed", tunnel_name.c_str());

orchagent/vxlanorch.h

@@ -484,6 +484,11 @@ class EvpnNvoOrch : public Orch2
         return source_vtep_ptr;
     }
 
+    void delEVPNVtep() 
+    { 
+        source_vtep_ptr = NULL;
+    }
+
 private:
     virtual bool addOperation(const Request& request);
     virtual bool delOperation(const Request& request);