Fix critical bug in new --enable-v4-mapped configure option

implementation which broke IPv4 listening sockets on
systems with IPV6_V6ONLY socket option.

That option should only be done on IPv6 listening sockets.

Submitted by:	hiroyuki hanai <hanai@imgsrc.co.jp>]
Reviewed by:	Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97595 13f79535-47bb-0310-9956-ffa450edef68