Create new function, ap_lingering_close(), which will explicitly do a lingering close

if USE_SO_LINGER is not defined. Move responsibility for closing connections out
of http_connection.c and into the MPMs.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85194 13f79535-47bb-0310-9956-ffa450edef68