Dont update device type to invalid, when interface configuration is d…

…eleted

Upon interface config deleting agent was setting device type of a VMI
to invalid, and if the device type is invalid, ip and evpn routes
were not getting deleted. Once device type is determined dont
update the type to invalid. test_intf already catches this case
Closes-bug:#1459124

Change-Id: I51e745db03fe3d39cce72470e3cf7d54635727ea

src/vnsw/agent/oper/vm_interface.cc

@@ -1668,7 +1668,8 @@ bool VmInterface::CopyConfig(const InterfaceTable *table,
         *ecmp_changed = true;
     }
 
-    if (device_type_ != data->device_type_) {
+    if (data->device_type_ !=  VmInterface::DEVICE_TYPE_INVALID &&
+        device_type_ != data->device_type_) {
         device_type_= data->device_type_;
         ret = true;
     }