LU-12931 ldlm: use proper units for timeouts

LU-12931 ldlm: use proper units for timeouts

Use timeout_t for ns_ctime_age_limit since this is a relative time
and not an absolute time.

Use ktime_t for ns_dirty_age_limit internally, even though the user
interface is in seconds, since this is frequenty used together with
other ktime_t values in the kernel.

Fixes: e920be681451 ("LU-9019 ldlm: migrate the rest of the code to 64 bit time")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Idb5ece834e56a95cd781cb871b1b7c20bf3ebbe5
Reviewed-on: https://review.whamcloud.com/38365
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>