BUG/MEDIUM: http-ana: apply tunnel timeout with data filters

BUG/MEDIUM: http-ana: apply tunnel timeout with data filters

The tunnel timeout is installed by process_stream() only once all
analysers are gone. HTTP data filters keep their transfer and end
analysers attached after a protocol upgrade. A stream using, for
example, set-bandwidth-limit therefore remains on its client and server
timeouts even though both HTTP messages are in tunnel mode. A short
client timeout can close a WebSocket before its heartbeat.

Apply the per-stream tunnel timeout when the second HTTP message enters
tunnel mode. Data-filter analysers remain active and continue to process
tunneled data.

It should be backported as far as 2.6.