Linux_5.0: replaced current_kernel_time with ktime_get_coarse_real_ts64

Linux_5.0: replaced current_kernel_time with ktime_get_coarse_real_ts64

In Kernel commit fb7fcc96a86cfaef0f6dcc0665516aa68611e736 the
current_kernel_time/current_kernel_time64 functions where renamed
and the calling was standardized.

According to the Linux Documentation/core-api/timekeeping.rst
ktime_get_coarse_real_ts64 is the direct replacement for
current_kernel_time64.  Because of year 2038 issues, there is no
replacement for current_kernel_time.

Updated code that used current_kernel_time to use new name and calling
convention.

Updated autoconf test that sets IATTR_TAKES_64BIT_TIME as well.

Reviewed-on: https://gerrit.openafs.org/13434
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 21ad6a0c826c150c4227ece50554101641ab4626)

Change-Id: Idb8a2c1b74835601fb1fc699c3ebbcee75c94e3e
Reviewed-on: https://gerrit.openafs.org/13442
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>