LU-6390 ldlm: restore the ELC for enqueue

LU-6390 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>
Change-Id: I19fb7c367d9d38107a4fb6d100a47c2e7b7ad640
Reviewed-on: http://review.whamcloud.com/14342
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Jenkins
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>