code: func setIPAMSerialAlloc(opts map[string]string) map[string]string {
  	if opts == nil {
  		opts = make(map[string]string)
  	}
  	if _, ok := opts[ipamapi.AllocSerialPrefix]; !ok {
  		opts[ipamapi.AllocSerialPrefix] = "true"
  	}
  	return opts
  }
docs: // setIPAMSerialAlloc sets the ipam allocation method to serial