Call the connected dns_dispatch callback asynchronously

Call the connected dns_dispatch callback asynchronously

The dns_request code is very sensitive about calling the connected and
deadlocks when the timing is "right" in several places.  Move the call
to the connected callback to the (udp|tcp)_connected() functions, so
they are called asynchronously instead of directly from
the (udp|tcp)_dispentry_cancel() functions.

(cherry picked from commit 9dd8deaf018cf7f93dc1d2ba08cc35764e76cc0f)