LU-12928 gss: crash in sec2target_str()

LU-12928 gss: crash in sec2target_str()

The timer_setup() API has being used since 3.10.0-957.x
kernel. So change gck_timer to a embedded struct to avoid
crashed on new timer API.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Ie12e21bca4169746016c8ac0e3ee4a125893ebf6
Reviewed-on: https://review.whamcloud.com/36708
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>