Ipv6

- Added .gitignore for object files.
- When Log DHCP queries is set to No, also add quiet-dhcp6 to dnsmasq's config file.
- ipv6_dhcp6s_enable was added in c82ebcf4e0383952322d0e35ba366b158fd29924, but it does not seem to be part of Asus mainline. I believe the equivalent for dnsmasq is to use ra-only when this nvram variable is set to 0.