Use APR_UNSPEC to allow startup on IP6-only systems.

PR: 50592
Submitted by: Joe Orton, 2510 <root linkage white-void net>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1146256 13f79535-47bb-0310-9956-ffa450edef68