LU-12603 ldlm: Check cancel lock count for correctness

LU-12603 ldlm: Check cancel lock count for correctness

Make sure the number of locks we are going to cancel fits into
the supplied buffer first.

Change-Id: I93887133532bf7ee2be27114b1972aa64e06623c
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reported-by: Alibaba Cloud <yunye.ry@alibaba-inc.com>
Reviewed-on: https://review.whamcloud.com/35806
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yunye Ry <yunye.ry@alibaba-inc.com>