LU-4653 fid: only compare non-IDIF seq in lu_fid_diff

LU-4653 fid: only compare non-IDIF seq in lu_fid_diff

Because it will pack OST index into IDIF FID in 2.6, and
in 2.4/2.5, the OST index in IDIF FID is always 0. So we
only compare non-IDIF sequence in lu_fid_diff.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I430210819c1cd7257094f51ef364f50d5291361c
Reviewed-on: http://review.whamcloud.com/9560
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>