(cherry picked from commit 725fcde)

• nat/bind/dhcp.service:
  Remove. Those services have nothing to do with a link-level service.

• sys-subsystem-net-devices-${if}.device:
  Add as BindsTo dependency as this will make hostapd stop when the
  device is unplugged.

• network-link-${if}.service:
  Add hostapd as dependency for this service via requiredBy clause,
  so that the network link is only considered to be established
  only after hostapd has started.

• network.target:
  Remove this from wantedBy clause as this is already implied from
  dependencies stacked above hostapd. And if it's not implied than
  starting hostapd is not required for this particular network
  configuration.

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• 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 nox --run "nox-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)
• Fits CONTRIBUTING.md.