Otherwise we get warnings like 'level=warning msg="failed to start
br_netfilter module"' in k3s's logs.
Adding modprobe to k3s's PATH fixes the warning at least. I'm not
certain if it fixes any real issue or not.
The upstream project already builds and releases for aarch64. This makes
the couple small tweaks that I found necessary for k3s to cross-compile
for aarch64.
I also ran it through nixpkgs-fmt.
This packages k3s as a single self-contained binary (as upstream k3s
does), but without having to download any impure already-built binaries.
The upstream packaging scripts are used. Due to k3s's rather complicated
packaging arrangement, this ends up being a rather long derivation.
