mod_proxy: allow SSLProxyCheckPeer* usage for all proxy modules.

PR 61857.

Proposed by: Markus Gausling <markusgausling googlemail.com>
Reviewed by: ylavic



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1818726 13f79535-47bb-0310-9956-ffa450edef68