task #28327019

Commit bc0cc360 ("alinux: blk-throttle: fix tg NULL pointer
dereference") add an self-defined bio flags to fix an issue of
use-after-free. But it is limited to 13 entry and has used up,
hence it will fails to sync related patch.

The patch replace reserved field with extended bio_flags to allow
us to define more bio flags.
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Nzhongjiang-ali <zhongjiang-ali@linux.alibaba.com>