UDP connection parameters are forgotten across app restarts

With the pixhawk streaming packets over UDP, I start the APM Planner and add a new UDP connection. I specify a port to listen, and then hit the "Add IP" button to set the IP and port number of the remove device. The connection immediately becomes active and I can both read and write to the Pixhawk.

If I restart the APM Planner, MAV link packets are still received and the UI reflects this, but I can no longer write mavlink packets to the device until I go back into the options for the UDP connection and re-enter the IP and port in the "Add IP" dialog.

Not working on both .15 and 16 RC3.

Start by reproducing the UDP connection setup, restart the APM Planner, and compare the saved connection state with the active runtime state. Trace where the listen port and remote IP/port from the "Add IP" dialog are persisted and restored; done means outbound MAVLink packets work after restarting without re-entering those values.

Written by the indexing model from the issue text.