File _service of Package libtommath

<services>
  <service name="download_src_package">
    <param name="host">vault.centos.org</param>
    <param name="protocol">http</param>
    <param name="path">/7.4.1708/extras/Source/SPackages/libtommath-0.42.0-6.el7.src.rpm</param>
  </service>
</services>