BUG/MEDIUM: stream: Report write timeouts before testing the flags

BUG/MEDIUM: stream: Report write timeouts before testing the flags

A regression was introduced when stream's timeouts were refactored. Write
timeouts are not testing is the right order. When timeous of the front SC
are handled, we must then test the read timeout on the request channel and
the write timeout on the response channel. But write timeout is tested on
the request channel instead. On the back SC, the same mix-up is performed.

We must be careful to handle timeouts before checking channel flags. To
avoid any confusions, all timeuts are handled first, on front and back SCs.
Then flags of the both channels are tested.

It is a 2.8-specific issue. No backport needed.