dnsmasq: configure dnsmasq via flat config file and not command-line args

Sometimes it's useful to compare the generated config file from UCI config with a hand-edited dnsmasq config file, especially if you're migrating to an OpenWRT router from something else (such as Astlinux).

Putting the generated config makes it easier to capture and diff, etc.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

SVN-Revision: 31182