dlm: use FL_SLEEP to determine blocking vs non-blocking

This patch uses the FL_SLEEP flag in struct file_lock to determine if
the lock request is a blocking or non-blocking request. Before dlm was
using IS_SETLKW() was being used which is not usable for lock requests
coming from lockd when EXPORT_OP_SAFE_ASYNC_LOCK inside the export flags
is set.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>