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

Change-Id: I95abd2cd2b777f99cbf6ab78370ee2171e5fca67
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/33963
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>