[20.03] nixos/initrd-network: always run postCommands

[Ma27]

Motivation for this change

Please note that fffd09d was needed to fix the initrd-network-ssh-test on release-20.03 which is why I filed a PR.

---

The backport of this patch has been requested in #79532[1]. The diff is
slightly off the original commit since some changes from
ea7d024 were needed, however this
commit shouldn't be backported as it potentially breaks existing setups.

[1] #79532 (comment)

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[mweinelt]

One could write code to boot.initrd.preLVMCommands and it will always be executed after networks is up or failed.

That would not really be intuitive, as you would now have to know the order in which things are executed in the initrd. 😐

[Ma27]

Doesn't it make postCommands useless because it starts duplicating boot.initrd.preLVMCommands

I generally agree with you, but this is a backport PR with a bugfix and I don't think we should delay this backport (of already reviewed code) because of that.

It's IMHO better to fix this on master first :)