Implement selective duplication remote control

[drblah]

In some cases we would like to only do selective duplication based on the radio conditions. Here we will have a primary and a secondary interface and we will only use the secondary connection when the primary connection is poor.

The base way to implement this is to have an exernal program perform measurements and then make a decision for us. Then tell us which interface(s) we should use.

Todo:

• [x] listen on a port UDP socket for control commands
• [x] Give Connections a boolean flag for enabled/disabled
• [x] Specify a communication format The command could look something like the following JSON:

{ "configs": [ { "interface_name": "eth0", "enabled": True } ] }

[drblah]

This is implemented in 971172e6f7e962e1ecec6748ea33e09e7357d7c6, e8a2ba61f7b666aac9eb26c38491a44387d47f94, c814b1b8c2b2b65ac41dfc0eaded056603d85f0a.

The format is binary encoded and implemented the same way as our regular tunnel messages, but it seems pretty easy to generate the bincode format using python.