LU-8560 llite: handle is_compat_task() rename

LU-8560 llite: handle is_compat_task() rename

The linux kernel 4.6 renamed is_compat_task() to
in_compat_syscall().

Change-Id: I2d3733a1ec03873d000b9f25aa8a98c3b02be410
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: http://review.whamcloud.com/22208
Reviewed-by: Frank Zago <fzago@cray.com>
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>