CVE-2021-3670 ldb: Confirm the request has not yet timed out in ldb filter processing

CVE-2021-3670 ldb: Confirm the request has not yet timed out in ldb filter processing

The LDB filter processing is where the time is spent in the LDB stack
but the timeout event will not get run while this is ongoing, so we
must confirm we have not yet timed out manually.

RN: Ensure that the LDB request has not timed out during filter processing
as the LDAP server MaxQueryDuration is otherwise not honoured.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14694

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>