luci-mod-network: DNS - support filtering A or AAAA records

Support Dnsmasq 2.87-5 feature to filter DNS results:
* remove IPv6 AAAA records and return only IPv4 addresses
* remove IPv4 A records and return only IPv6 addresses

Especially the removal of IPv6 AAAA records can be useful with
ISPs that provide IPv6 address resolving but do not actually
offer IPv6 routing/connectivity.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>