• When HTTP/2 flow controls blocks further writes, return processing to an
  async mpm to free a worker thread. The connection needs window updates from
  the client in such a case and can leave monitoring the socket to the mpm.
  So far, only effective on Apache httpd 2.5.0 (trunk).
  [ylavic, icing]
• Backport fix of CVE-2024-36387 from Apache 2.4.60.