LU-15683 ofd: proper initialize filter_fid in ofd fallocate

LU-15683 ofd: proper initialize filter_fid in ofd fallocate

Intialize filter_fid buffer and call xattr set XATTR_NAME_FID properly
in ofd_object_fallocate().

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Ied573c39dde77f935622e9fbedb2d71eb3bd8f5d
Reviewed-on: https://review.whamcloud.com/46919
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>