Set dhcp-authoritative so clients with unexpired leases are not NAKed
after a router crash or factory reset that clears the lease database.
Drop the untagged suppress directives for options 3 (router) and 6
(dns-server): they conflict with the global options confd writes to
dnsmasq.d/, causing spurious "Ignoring duplicate dhcp-option" warnings.
Per-subnet tagged options already suppress auto-detection, and without
an active dhcp-range there is nothing to suppress anyway.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>