LU-12568 lnet: Defer rspt cleanup when MD queued for unlink

LU-12568 lnet: Defer rspt cleanup when MD queued for unlink

When an MD is queued for unlink its lnet_libhandle is invalidated so
that future lookups of the MD fail. As a result, the monitor thread
cannot detach the response tracker from such an MD, and instead must
wait for the remaining operations on the MD to complete before it can
safely free the response tracker and remove it from the list. Freeing
the memory while there are pending operations on the MD can result
in a use after free situation when the final operation on the MD
completes and we attempt to remove the response tracker from the MD
via the lnet_msg_detach_md()->lnet_detach_rsp_tracker() call chain.

Here we introduce zombie lists for such response trackers. This will
allow us to also handle the case where there are response trackers
on the monitor queue during LNet shutdown. In this instance the
zombie response trackers will be freed when either all the operations
on the MD have completed (this free'ing is performed by
lnet_detach_rsp_tracker()) or after the LND Nets have shutdown since
we are ensured there will not be any more operations on the
associated MDs (this free'ing is performed by
lnet_clean_zombie_rstqs()).

Three other small changes are included in this patch:
 - When deleting the response tracker from the monitor's list we
   should use list_del() rather than list_del_init() since we'll
   be freeing the response tracker after removing it from the list.
 - Perform a single ktime_get() call for each local queue.
 - Move the check of whether the local queue is empty outside of
   the net lock.

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: I2a62ceb5b259a094204a1500527443e942483386
Reviewed-on: https://review.whamcloud.com/35576
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>