Fix MapLinkPayload to account for offset

If you like it, great, but mostly wanted to point out that I think this would be pretty easy to fix, without breaking anything.

Also hoping the comments make it easier to understand.

I was staring at this for too long I think trying to make sense of it, so be merciful 🙂

You may want to rebase this one against the net5 branch, master is already on net6 and not mainline, currently

@goaaats Sorry, life kinda got in the way. It's been a while since your comment about net5 (pretty sure net6 is mainline now), let me know if you need me to do anything.