==== update_descriptor

Defined by DVB in <<ETSI-102-006>>.
Must be in a UNT (table id 0x4B).

[source,xml]
----
<update_descriptor
    update_flag="uint2, required"
    update_method="uint4, required"
    update_priority="uint2, required">

  <private_data>
    Hexadecimal content
  </private_data>

</update_descriptor>
----
