fff-dhcp: Add configuration scripts for dns

Because DNS Forwarding is done by dnsmasq which we configure
inside the fff-dhcp package, the configuration scripts for dns
are placed in this package.

Signed-off-by: Fabian Bläse <fabian@blaese.de>
Reviewed-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>