Minor bug in service state management

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1598555 13f79535-47bb-0310-9956-ffa450edef68
Expose listener endpoint

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1598560 13f79535-47bb-0310-9956-ffa450edef68