code: public DnsManager putHosts(String domain, String ip, int provider) {
          hosts.put(domain, new Hosts.Value(ip, provider));
          return this;
      }
docs: 插入指定运营商的hosts配置
  
  @param domain   域名
  @param ip       ip
  @param provider 运营商，见 NetworkInfo
  @return 当前的DnsManager，便于链式调用