code: func NetworkInterfaceDiffOperation(d *schema.ResourceDiff, c *govmomi.Client) error {
  	// We just need the new values for now, as all we are doing is validating some values based on API version
  	n := d.Get(subresourceTypeNetworkInterface)
  	log.Printf("[DEBUG] NetworkInterfaceDiffOperation: Beginning diff validation")
  	for ni, ne := range n.([]interface{}) {
  		nm := ne.(map[string]interface{})
  		r := NewNetworkInterfaceSubresource(c, d, nm, nil, ni)
  		if err := r.ValidateDiff(); err != nil {
  			return fmt.Errorf("%s: %s", r.Addr(), err)
  		}
  	}
  	log.Printf("[DEBUG] NetworkInterfaceDiffOperation: Diff validation complete")
  	return nil
  }
docs: // NetworkInterfaceDiffOperation performs operations relevant to managing the
  // diff on network_interface sub-resources.