nixos: Add tcpdump on all machines

nixos/modules/common.nix

@@ -139,6 +139,7 @@ in
           bash-completion
           git
           unzip
+          tcpdump
         ]
         (mkIf config.services.netdata.enable [ netdata ])
       ];

nixos/modules/server.nix

@@ -36,10 +36,6 @@ in
     };
 
     documentation.nixos.enable = mkDefault' false;
-
-    environment.systemPackages = with pkgs; [
-      tcpdump
-    ];
   };
 
   meta.buildDocsInSandbox = false;