- according to https://www.apachelounge.com/Changelog-2.4.html,
modules should be updated to inquire for ap_get_useragent_host()
in place of ap_get_remote_host().
- use module magic number 20120211,56 to determine whether to use ap_get_useragent_host
(according to https://github.com/apache/httpd/blob/2.4.x/include/ap_mmn.h)