LU-6215 gss: key->payload.data is an array in 4.4+ kernels

LU-6215 gss: key->payload.data is an array in 4.4+ kernels

Kernel 4.4 merged the type-specific data with the payload data
for keys, as a result, payload.data is now an array.
This patch handles the code change.

Linux-commit: 146aa8b1453bd8f1ff2304ffb71b4ee0eb9acdcc

Signed-off-by: Li Dongyang <dongyang.li@anu.edu.au>
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: I1036ab927514f0efa073d9f0136e299be8950461
Reviewed-on: http://review.whamcloud.com/18731
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>