async_socket_for_remote/use_hedged_requests uses nested epolls, which
may not be reliable in 5.5+ [1], but it has been fixed in shortly in
5.7+ [2] or
5.6.13+.

  [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=339ddb53d373
  [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0c54a6a44bf3