When no UDP listeners are present, skip the UDP health-check code
branch, which prevents expensive and unnecessary DB calls.
Also optimise the UDP health-check code so it only fetches information
for relevant listeners.
Co-Authored-By: Adam Harwell <flux.adam@gmail.com>
Change-Id: I7fde54084b39c1d0529cfb0bcfb79697d63ea6ae
(cherry picked from commit 24e77d606d)