Determine actual SeedLink packet sizes at run time instead of hardcoding SeedLink packet sizes to the SLRECSIZE const at compile time

[yensoon2]

Good morning @chad-iris,

I’ve updated my pull request so that it now builds against libslink 2020.048 or later.

When will you release the next version of slinktool?

Thank you very much for your efforts,

@yen-soon