All the experts will tell you - don't attempt to paper over woodchip, the result will look awful, and don't even think about putting a plaster skim over it - you risk it wetting the old paste , and you could end up with areas drooping down. Alas, the only way is to remove the woodchip paper.
You'd be best using a
scorer going gently over the whole surface of the woodchip. You could use a Stanley knife, but this would be a lot of work, and you'd risk damaging the plaster. Then, use a steam wallpaper stripper. The idea is to soften the woodchip so that it will lift off easily with a minimum of scraping pressure, and without disturbing the plaster.