Let Nether manage UDPLite traffic and local DNS queries

Let Nether manage UDPLite traffic and local DNS queries

A netfilter rule has been added to let Nether manage UDPLite traffic for
outgoing connections. There are some kernel configurations that don't have
NF_CT_PROTO_UDPLITE option turned on. For these kernel images, the rule that
uses the conntrack module do not catch packets of the UDPLite protocol.
Special rules have been introduced to inspect DNS queries sent by an app
to the Connman service (running on localhost). The Connman service, which
works as a DNS proxy, sends the queries out of the box on behalf
of the app.

Change-Id: Ib41e61d8367b8c78eb814b3e98396e6c1e5fa4b1