MEDIUM: stream-int: automatically disable CF_STREAMER flags after idle

MEDIUM: stream-int: automatically disable CF_STREAMER flags after idle

Disabling the streamer flags after an idle period will help TCP proxies
to better adapt to the streams they're forwarding, especially with SSL
where this will allow the SSL sender to use smaller records. This is
typically used to optimally relay HTTP and derivatives such as SPDY or
HTTP/2 in pure TCP mode when haproxy is used as an SSL offloader.

This idea was first proposed by Ilya Grigorik on the haproxy mailing
list, and his tests seem to confirm the improvement :

  https://www.mail-archive.com/haproxy@formilux.org/msg12576.html