Hemisphere GPS on ArduRover

Trying to use HDT-messages from a Hemisphere GPS for heading, instead of the build-in compass.
We’ve checked out https://github.com/tridge/ardupilot_wiki.git
./waf configure --board blue
./waf rover
and installed it on a Beaglebone Blue, but MissionPlanner does not seem to see GPS type 16 as described at https://github.com/ArduPilot/ardupilot/pull/7215
What did we miss?

We have a Hemisphere GPS that outputs real Heading in NMEA HDT messages, and that heading is much, much more accurate than Blues internal magnetic compass.