mod_remoteip: make proxy-protocol work on slave connections, e.g. in HTTP/2

     requests. See also https://github.com/roadrunner2/mod-proxy-protocol/issues/6


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1827196 13f79535-47bb-0310-9956-ffa450edef68