Kfuncs (kernel functions) are the new replacement for helper functions, as such we should start documenting these as well. Doing so is slightly more challenging since there are no man-page docs for these that we can reuse yet.
### Tasks
- [x] Add a linux/concepts page for kfuncs to go into depth on how to use them
- [x] Add a section to the "eBPF on Linux" page
- [x] Add index of kfunc programs sorted by type (comparable to helper functions)
- [x] Add tooling to generate kfunc -> program type
- [x] Add kfuncs to feature-version.yaml
- [x] Add kfuncs to quick links
- [x] Add tooling to generate function signatures (possible via vmlinux BTF blobs)
- [x] Add pages for known kfuncs, attempt to write a little context if possible
- [x] Add tooling to generate program type -> kfunc lists
Kfuncs (kernel functions) are the new replacement for helper functions, as such we should start documenting these as well. Doing so is slightly more challenging since there are no man-page docs for these that we can reuse yet.