When running on routers, ctrld leverages default setup, let dnsmasq runs
on port 53, and forward queries to ctrld listener on port 5354. However,
this setup is not serialized to config file, causing confusion to users.
Fixing this by writing the correct routers setup to config file. While
at it, updating documentation to refelct that, and also adding note that
changing default router setup could break things.
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