LU-12477 lustre: restore time_after32()

LU-12477 lustre: restore time_after32()

time_after32 is needed when compiling with kernels earlier than v4.14,
which haven't had it backported.  E.g. SLE12-SP3-LTSS needs it.

Fixes: 8e88bbfef579 ("LU-12477 lustre: remove obsolete config checks")
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ifb51b9ed0945ad28f8e8aa34dada3860107b95df
Reviewed-on: https://review.whamcloud.com/37725
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>