BUG/MINOR: stream: Fix test on channels flags to set clientfin/serverfin touts

BUG/MINOR: stream: Fix test on channels flags to set clientfin/serverfin touts

There is a bug in a way the channels flags are checked to set clientfin or
serverfin timeout. Indeed, to set the clientfin timeout, the request channel
must be shut for reads (CF_SHUTR) or the response channel must be shut for
writes (CF_SHUTW). As the opposite, the serverfin timeout must be set when
the request channel is shut for writes (CF_SHUTW) or the response channel is
shut for reads (CF_SHUTR).

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