code: public OperationFuture<List<Server>> modifyPublicIp(ServerFilter filter, ModifyPublicIpConfig config) {
          return modifyPublicIp(Arrays.asList(getRefsFromFilter(filter)), config);
      }
docs: Modify existing public IP on servers
  @param filter The server filter object
  @param config  publicIp config
  @return OperationFuture wrapper for list of ServerRef