core: If explicitly configured, use the KeepaliveTimeout value of the

virtual host which handled the latest request on the connection, or by
default the one of the first virtual host bound to the same IP:port.

For non-async MPMs, use either r->server's or c->base_server's value in
ap_process_http_sync_connection() depending on a new server_rec's flag
called keep_alive_timeout_set and determined at config time.

For event MPM, use a queue per timeout value, chaining the queues per
type (keepalive wrt KeepAliveTimeout, write completion wrt to Timeout)
so that maintenance can be done on all the queues from the head, and such
that insertions/maintenance remain in O(1).
A server config is created and pointing to the queue of each vhost at
post_config time, hence the config can be associated to the connection
state (cs) at post_read_request time, and we can simply insert with
TO_QUEUE_INSERT(cs->sc->q, cs).  PR56226.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1664071 13f79535-47bb-0310-9956-ffa450edef68