LU-9660 ptlrpc: do not wakeup every second

LU-9660 ptlrpc: do not wakeup every second

Even if there are no RPC requests on the set, there is no need to
wake up every second. The thread is woken up when a request is added
to the set or when the STOP bit is set, so it is sufficient to only
wake up when there are requests on the set to worry about.

Change-Id: Iac01d8c46e8645ecb6303ce72e0f6c59f16dcd5d
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: https://review.whamcloud.com/28776
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>