Partially initialized lock (without l_ast_data to be init)
caused a fail with blocking ast, as discard from page cache
skipped, and stale data will read later with fast read.
Slow read have chance to attach this lock to right IO, but
it don’t true always, so that should disabled, until lock
will have l_ast_data set always for DoM and Lock Ahead locks.

HPE-bugid: LUS-8750
Change-Id: I2c5180c8044a12d7bd8f5f1c871447ca8b47a8ff
Signed-off-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-on: https://review.whamcloud.com/39318


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Vitaly Fertman <vitaly.fertman@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>