LU-2675 cleanup: const correct FID/OSTID/... helpers

LU-2675 cleanup: const correct FID/OSTID/... helpers

Add a const qualifier wherever possible to the pointer parameters of
the inline helper functions in lustre_idl.h and lustre_fid.h. Change
the return type of several predicate functions from int to bool.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ibe590d7184470cfe8a154fe0935a7d6bea261669
Reviewed-on: http://review.whamcloud.com/8641
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>