LU-11848 filefrag: rework port PFL and FLR file

LU-11848 filefrag: rework port PFL and FLR file

Lustre uses the high 16bits of fiemap_extent:fe_device to record
the absolute stripe number is under process, so that next fiemap
call continues from that stripe.

Fixes: 0b6718f5e22d ("filefrag: support PFL and FLR file")
Change-Id: I111bcb100307aebacbffed99109057accdc27f5b
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/40889
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>