AP_Mount: added sending of position and velocity to Siyi

[tridge]

This will allow for exif tags in photos with position of aircraft

[rmackay9]

I tested this on a Siyi A8 running the latest Siyi firmware (0.3.4) and it seems fine.

[rmackay9]

I will test that the EXIF works on an A8

[rmackay9]

@tridge,

I tested with the SiyiA8 running the latest gimbal and camera firmwares (0.3.7 and 0.2.6 respectively) and while it all seems to basically work (e.g the gimbal moves, pictures and videos are recorded), the EXIF does not include the vehicle's location

[rmackay9]

I've taken the devCall tag off of this one because we've since had a discussion with Siyi and there have been some changes to their API.

[rmackay9]

Hi @tridge,

Could you replace the contents of the PR with the last commit from this branch? https://github.com/rmackay9/rmackay9-ardupilot/commits/tridge-siyi-position/

The code in this PR fails to send the location because it exceeds the maximum packet length. With this fix, I've confirmed that the A8 does store the correct location into the images (aka EXIF)

There appears to be an issue on the Siyi side with the altitude appearing as "Below" Sea Level but hopefully that can be resolved on their side.

[rmackay9]

Let's close this in favour of #27457