add support for setting up routing inside the netns

nix/module.nix

@@ -60,6 +60,22 @@ in {
             default = [];
             description = "devices to move into the namespace";
           };
+          route = mkOption {
+            type = types.listOf (types.submodule ({config, ...}: {
+              options = {
+                device = mkOption {
+                  type = types.str;
+                  description = "device to route the traffic trough";
+                };
+                destination = mkOption {
+                  type = types.str;
+                  description = "What traffic to route. Either \"default\" or an ip range in CIDR notation";
+                };
+              };
+            }));
+            description = "routes to setup inside the namespace";
+            default = [];
+          };
         };
       }));
       description = "namespaces to setup";