nixos: add programs.wireshark option

To be able to use Wireshark as an ordinary user, the 'dumpcap' program
must be installed setuid root. This module module simplifies such a
configuration to simply:

programs.wireshark.enable = true;

The setuid wrapper is available for users in the 'wireshark' group.

Changes v1 -> v2:
- add "defaultText" to the programs.wireshark.package option (AFAIK,
that prevents the manual from being needlessly rebuilt when the
package changes)

nixos/modules/misc/ids.nix

···
       kresd = 270;
       rpc = 271;
       geoip = 272;
+      #wireshark = 273; # unused
 
       # When adding a uid, make sure it doesn't match an existing gid. And don't use uids above 399!
 
···
       kresd = 270;
       #rpc = 271; # unused
       #geoip = 272; # unused
+      wireshark = 273;
 
       # When adding a gid, make sure it doesn't match an existing
       # uid. Users and groups with the same name should have equal

nixos/modules/module-list.nix

···
   ./programs/tmux.nix
   ./programs/venus.nix
   ./programs/vim.nix
+  ./programs/wireshark.nix
   ./programs/wvdial.nix
   ./programs/xfs_quota.nix
   ./programs/xonsh.nix

nixos/modules/programs/wireshark.nix

···
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.wireshark;
+  wireshark = cfg.package;
+
+in
+
+{
+
+  options = {
+
+    programs.wireshark = {
+
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether to add Wireshark to the global environment and configure a
+          setuid wrapper for 'dumpcap' for users in the 'wireshark' group.
+        '';
+      };
+
+      package = mkOption {
+        type = types.package;
+        default = pkgs.wireshark-cli;
+        defaultText = "pkgs.wireshark-cli";
+        description = ''
+          Which Wireshark package to install in the global environment.
+        '';
+      };
+
+    };
+
+  };
+
+  config = mkIf cfg.enable {
+
+    environment.systemPackages = [ wireshark ];
+    
+    security.wrappers.dumpcap = {
+      source = "${wireshark}/bin/dumpcap";
+      owner = "root";
+      group = "wireshark";
+      setuid = true;
+      setgid = false;
+      permissions = "u+rx,g+x";
+    };
+
+    users.extraGroups.wireshark.gid = config.ids.gids.wireshark;
+
+  };
+
+}