LU-11838 kernel: harden current_time autoconf test

LU-11838 kernel: harden current_time autoconf test

In newer kernels CURRENT_TIME was replaced by current_time(). The
return value of current_time() was struct timespec but to support
time after 2038 the return value was changed to struct timespec64.
This change broke the autoconf test. The solution is to use one
of the struct iattr field in the autoconf test since it hides
the return value type.

Test-Parameters: trivial

This patch is back-ported from the following one:
Lustre-commit: 74b3726f42b1f72e289e3c3252030a62646afa7b
Lustre-change: https://review.whamcloud.com/33963

Change-Id: I95abd2cd2b777f99cbf6ab78370ee2171e5fca67
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-on: https://review.whamcloud.com/35170
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>