LU-8352 libcfs: Migrate file_inode() wrapper to lustre layer

LU-8352 libcfs: Migrate file_inode() wrapper to lustre layer

The file_inode() defined in libcfs will collide with the
same defination in compat-2.6.h from the OFED/Mellanox
stack. The easiest way to avoid this is move the file_inode
wrapper from libcfs linux-fs.h header to lustre_compat.h.
The header lustre_compat.h is only used in the lustre
layer so it wouldn't collide with compat-2.6.h.

Change-Id: I70502be0d824a2a1f9c538ae894ab8183961349b
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: http://review.whamcloud.com/21082
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Reviewed-by: Chris Horn <hornc@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>