BUG/MEDIUM: streams: Don't remove the SI_FL_ERR flag in si_update_both().

BUG/MEDIUM: streams: Don't remove the SI_FL_ERR flag in si_update_both().

Don't inconditionally remove the SI_FL_ERR code in si_update_both(), which
is called at the end of process_stream(). Doing so was a bug that was there
since the flag was introduced, because we were always setting si->flags to
SI_FL_NONE, however we don't want to lose that one, except if we will retry
connecting, so only remove it in sess_update_st_cer().

This should be backported to 1.9.