staging/lustre/lnet: NI shutdown may loop forever

lnet_shutdown_lndnis() may enter endless loop if there is a busy NI,
this is injected by LNet SMP improvements. It's fixed in this patch.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Reviewed-on: http://review.whamcloud.com/9706
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4780


Reviewed-by: Isaac Huang <he.huang@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>