Switch to the new API for delayed work related to DNS queries.
In the previous solution it was assumed that the work item could be
immediately cancelled at the point the query slot was released. This
is not true. We need a secondary condition to record the fact that
the query was completed while the work item was still pending, and an
additional check to detect when the work item completed and the slot
reclaimed.
Also annotate functions to indicate when they require the lock on
query content to be held, add some helpers that abstract core
operations like invoking a callback or releasing a query slot, and fix
some more cases where query slot content was accessed outside of the
new lock infrastructure.
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
1c7bf96019