LU-8209 ldlm: engage ELC for all ldlm enqueue req

LU-8209 ldlm: engage ELC for all ldlm enqueue req

If there is no request passed into ldlm_cli_enqueue, the enqueue
request will not engage ELC to drop unneeded locks. currently,
this kind of request is mainly related to EXTENT locks enqueue
requests (except for glimpse EXTENT lock for it has an intent).

Change-Id: Ibb34117cbec6764f643457d9b0af142393263608
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/21739
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Vitaly Fertman <vitaly.fertman@seagate.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>