zebra: Ensure dplane does not send work back to master at wrong time

zebra: Ensure dplane does not send work back to master at wrong time

When looping through the dplane providers, the worklist was
being populated with items from the last provider and then
the event system was checked to see if we should stop processing.
If the event system says `yes` then the dplane code would stop
and send the worklist to the master zebra pthread for collection.
This obviously skipped the next dplane provider on the list
which is double plus not good.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>