Update link_drain with new kernel method

Now we are dealing with link-drain in a much simpler way,
so the test program is updated as well.

Also fixed a bug that did not close fd when an error occurred.
and some dead code has been modified, like commit e1420b89c do.

Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 file changed