LU-9468 llite: fix for stat under kthread and X86_X32

LU-9468 llite: fix for stat under kthread and X86_X32

Under the following conditions, ll_getattr will flatten the inode
number when it shouldn't:

  - the X86_X32 architecture is defined CONFIG_X86_X32, and not even
    used,
  - ll_getattr is called from a kernel thread (though vfs_getattr for
    instance.)

This has the result that inode numbers are different whether the same
file is stat'ed from a kernel thread, or from a syscall. For instance,
4198401 vs. 144115205272502273.

ll_getattr calls ll_need_32bit_api to determine whether the task is 32
bits. When the combination is kthread+X86_X32, that function returns
that the task is 32 bits, which is incorrect, as the kernel is 64
bits.

The solution is to check whether the call is from a kernel thread
(which is 64 bits) and act consequently.

Added test_410 to test the condition. A failed run will have a message like this:

  lustre_kinode_54354: CONFIG_X86_X32 is set
  lustre_kinode_54354: inode is 144115205272502273
  lustre_kinode_54354: inode is 4198401
  lustre_kinode_54354: inode numbers are different: 144115205272502273 4198401

while a successfull one will be:

  lustre_kinode_10519: CONFIG_X86_X32 is set
  lustre_kinode_10519: inode is 144115205272502275
  lustre_kinode_10519: inode is 144115205272502275
  lustre_kinode_10519: inode numbers are identical: 144115205272502275

Signed-off-by: Frank Zago <fzago@cray.com>
Change-Id: Ib8f07de47eaa29046a61c488368d466f9096a994
Reviewed-on: https://review.whamcloud.com/26992
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>