code: func (f *ConntrackFilter) AddIP(tp ConntrackFilterType, ip net.IP) error {
  	if f.ipFilter == nil {
  		f.ipFilter = make(map[ConntrackFilterType]net.IP)
  	}
  	if _, ok := f.ipFilter[tp]; ok {
  		return errors.New("Filter attribute already present")
  	}
  	f.ipFilter[tp] = ip
  	return nil
  }
docs: // AddIP adds an IP to the conntrack filter