Adds ocaml-cmdliner

Cmdliner is an OCaml module for the declarative definition of command
line interfaces.

Homepage: http://erratique.ch/software/cmdliner
s6-portable-utils: new package

s6-portable-utils is a set of tiny general Unix utilities, often
performing well-known tasks such as cut and grep, but optimized for
simplicity and small size.
s6-dns: new package

s6-dns is a suite of DNS client programs and libraries for Unix systems,
as an alternative to the BIND, djbdns or other DNS clients.
s6-networking: new package

s6-networking is a suite of small networking utilities for Unix systems
including UCSPI Unix and TCP tools, access control tools, and network
time management utilities.
s6-linux-utils: new package

s6-linux-utils is a set of minimalistic Linux-specific system utilities.
Don't specify Perl version
nixos/network-interfaces: Implement the ability to add routes
nixos/network-interfaces: Don't restart network interfaces as routing happens per if
nixos/network-interfaces: Warn about using deprecated defaultGateway
nixos/network-interfaces: Pick the best default gateway interface
nixos/network-interfaces: Validate the subnets for ipv4 routes