ap-dnsproxy: keep networkcache lines unique
ap-dnsproxy: networkcache exists always, it's just emptied when handled
ap-dnsproxy: suppress noise and document a hack
ap-dnsproxy: fix typo
ap-dnsproxy: maintain the list of networks always

The list is used to disable all DNS redirections on exit.
ap-dnsproxy: add comment to iptables rules to distinguish them from other rules