Added logic to the worker MPM to skip the poll before accept

if there's only one listener socket (based on the implementation
in the prefork MPM).  This also enables us to do single-listener
unserialized accept


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93096 13f79535-47bb-0310-9956-ffa450edef68