Small style fixups

In this commit, I modified some files, conforming them to a
idiosyncratic standard - mainly, a template for meta attribs.
add functor-infix
Merge pull request #4046 from phunehehe/add-functor-infix

add functor-infix
Merge pull request #4030 from AndersonTorres/small-fixups

Small style fixups
nixos/ssh: Allow user to configure the package that provides ssh/sshd