ab: Work over non-loopback on Unix again.

(Broken as of 2.0.47 due to dependence on an APR bug which was fixed
in 2.0.47.)

PR:   21495


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@100846 13f79535-47bb-0310-9956-ffa450edef68