Fix address-in-use startup failure caused by corruption of the list of

Fix address-in-use startup failure caused by corruption of the list of
listen sockets in some configurations with multiple generic Listen
directives.

The logic in error is that which prunes out generic IPv4 listening
sockets when we already have a v4-mapped generic IPv6 listening
socket for the same port.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@467034 13f79535-47bb-0310-9956-ffa450edef68