Allow zstd compression level up to 22

[Bisaloo]

The latest documentation states:

The library supports regular compression levels from 1 up to ZSTD_maxCLevel(),
which is currently 22. Levels >= 20, labeled --ultra, should be used with
caution, as they require more memory. The library also offers negative
compression levels, which extend the range of speed vs. ratio preferences.
The lower the level, the faster the speed (at the cost of compression).

https://facebook.github.io/zstd/doc/api_manual_latest.html