dnsmasq: Listen only on loopback and disable DHCP

Dnsmasq functions as DHCP and DNS servers by default and listens on all
interfaces. This conflicts with other DHCP or DNS servers already on
the network and corrupts DNS configuration on Windows systems.

We noticed that after installing docker, the Linux system became a
magnet for DNS requests coming from Windows systems. Dnsmasq is a
dependency for lxc which is recommended for docker.

Windows periodically broadcasts DHCPInform and DHCP servers reply with
DHCPAck. If the DHCPAck from the Linux target reaches the Windows
system first, Windows changes its DNS server IP to the Linux system
running dnsmasq. Dnsmasq ends up forwarding the DNS requests to the
official DNS server and replies back the answer to the original
requestor. The Linux system transparently becomes a DNS proxy on the
subnet.

Signed-off-by: Ovidiu Vancea <ovidiu.vancea@ni.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>