add support for MAV_TYPE = 11 (boats)

[rmackay9]

At least one user of ArduPilot with ROS has said that they cannot change flight modes and are receiving this message, “MODE: Unknown APM Based FCU! Type 11”.

ArduPilot has recently added proper support for Boats but using the Rover firmware. The differences between the two vehicle types is all contained within ArduPilot so from a ROS/mavros point of view it should be fine to treat Type 11 (boats) the same as Type 10 (ground rovers)

Thanks!

[TSC21]

https://github.com/mavlink/mavros/blob/master/mavros/src/lib/uas_stringify.cpp#L201
PR welcomed ;)

[vooon]

@rmackay9 done. Can you test it?

[rmackay9]

@vooon, thanks very much! Yes, i will try it or more likely i will find someone who knows this more than i do. Txs again!