LU-17013 lov: fill FIEMAP_EXTENT_LAST flag

LU-17013 lov: fill FIEMAP_EXTENT_LAST flag

If file has N extents and get the fiemap with exactly N
extent slots, the last extent will miss FIEMAP_EXTENT_LAST
flag. Fix it.

Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: testlist=sanityn env=ONLY=71a+71b+71c
Change-Id: I4556b31f0d04bdf8e83f323e83b871b093beaa5e
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51863
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>