bus: update kdbus.h (ABI break)

We changed creds to u32, so fix systemd sd-bus to acknowledge that.
update TODO
update TODO
sd-bus: given that the kernel now passes the auxgroups list as 32bit array to us, no need to convert to uid_t manually

This way, we can save one allocation and avoid copying the array
unnecesarily.
update TODO
update TODO
core: reindent mount/kmod tables
sd-bus: update kdbus.h from upstream