LU-6769 build: Test for kthread_worker support

LU-6769 build: Test for kthread_worker support

The OFED compatibility layer will backport kthread_worker unless
CONFIG_COMPAT_IS_KTHREAD is defined. kthread_worker is available in
the SLES 11 SP3 kernel, but not RHEL 6.5 or RHEL 6.6. This mod adds a
test to check if kthread is available in the kernel and defines
CONFIG_COMPAT_IS_KTHREAD appropriately.

Later versions of MLNX_OFED (2.4, 3.0) require that we similarly
define HAVE_KTHREAD_WORK.

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ia89b73e4c8a3ad8549efdea70f0ebd96a1151dba
Reviewed-on: http://review.whamcloud.com/15428
Tested-by: Jenkins
Reviewed-by: Shuichi Ihara <sihara@ddn.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>