Change prefork to use the same listen api as the rest of the unix mpms

(ap_setup_listeners).  This eliminates the need to force a recompile of
listen.c when you switch to/from using prefork.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86179 13f79535-47bb-0310-9956-ffa450edef68