nixos/tinc: do not add Device= by default

tinc can figure this out based on DeviceType.
I also got `/dev/net/tun FD in bad state` after a particular upgrade.

Changed files
-1
nixos
modules
services
networking
-1
nixos/modules/services/networking/tinc.nix
···
${optionalString (data.ed25519PrivateKeyFile != null) "Ed25519PrivateKeyFile = ${data.ed25519PrivateKeyFile}"}
${optionalString (data.listenAddress != null) "ListenAddress = ${data.listenAddress}"}
${optionalString (data.bindToAddress != null) "BindToAddress = ${data.bindToAddress}"}
-
Device = /dev/net/tun
Interface = tinc.${network}
${data.extraConfig}
'';