Propagate the shutdown event to the recursing ns_client(s)

Propagate the shutdown event to the recursing ns_client(s)

Send the ns_query_cancel() on the recursing clients when we initiate the
named shutdown for faster shutdown.

When we are shutting down the resolver, we cancel all the outstanding
fetches, and the ISC_R_CANCEL events doesn't propagate to the ns_client
callback.

In the future, the better solution how to fix this would be to look at
the shutdown paths and let them all propagate from bottom (loopmgr) to
top (f.e. ns_client).