LU-9859 libcfs: add watchdog for ptlrpc service threads.

LU-9859 libcfs: add watchdog for ptlrpc service threads.

If a ptlrpc thread takes longer than expected, it
can be used to get a stack trace to see where the
problem is.

This patch moves this functionality out of libcfs
by using a delayed work struct to report a back
trace of the thread if it ever fires.

Change-Id: I8f54df430322f0751b179f67284018e576defc08
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/33018
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>