kernel: delayed_work: update k_delayed_work_cancel documentation

Although the documentation states that only work items that have not
completed the delay can be cancelled, in fact pending items can also
be removed from a work queue.  Document that behavior

Also document the specific return value that will be obtained based on
the state of the work item at the time cancellation was attempted
using the current implementation.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
2 files changed