staging/lustre/ldlm: restore the ELC for enqueue

after LU-4300 enqueue does not ELC anymore, however if enqueue is
agressive (ls -la of a large dir) we may exceed lru-resize limit
quickly because LRUR shrinker and recalc are called not so often.

ELC is to be restored in enqueue.
ELC also should check for the lock weight, in addition to LRUR.
ELC can also keep "skipped" locks, i.e. once checked for the weight
and left in the lru - let LRUR take care about them later.
LRUR is to be left untouched, no weight logic, otherwise LU-5727
appears and OPEN locks do not get canceled.

Xyratex-bug-id: MRP-2550
Signed-off-by: Vitaly Fertman <vitaly.fertman@seagate.com>
Reviewed-on: http://review.whamcloud.com/14342
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6390


Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>