nixos/printers: fix ensureDefaultPrinter

`lpoptions -d` sets the default printer *for this user*, while `lpadmin -d`
sets the system-wide default printer.

Changed files
+1 -1
nixos
modules
hardware
+1 -1
nixos/modules/hardware/printers.nix
···
${ppdOptionsString p.ppdOptions}
'';
ensureDefaultPrinter = name: ''
-
${pkgs.cups}/bin/lpoptions -d '${name}'
+
${pkgs.cups}/bin/lpadmin -d '${name}'
'';
# "graph but not # or /" can't be implemented as regex alone due to missing lookahead support