LU-6215 gss: cache_head is now on a hlist in 4.3+ kernels

LU-6215 gss: cache_head is now on a hlist in 4.3+ kernels

Since kernel 4.3 struct cache_head switched from a single
list to a hlist. This patch handles the change.

Linux-commit: 129e5824cd96d9289679973f0ff7c48e88d569bb

Signed-off-by: Li Dongyang <dongyang.li@anu.edu.au>
Change-Id: Iec4c7d0acf106a8f7b60d72eb2038b6d9e12f422
Reviewed-on: http://review.whamcloud.com/18728
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>