nixos/mullvad-vpn: fix firewall issues & remove xfix as maintainer

nixos/modules/services/networking/mullvad-vpn.nix

@@ -9,6 +9,7 @@ with lib;
     default = false;
     description = ''
       This option enables Mullvad VPN daemon.
+      This sets <option>networking.firewall.checkReversePath</option> to "loose", which might be undesirable for security.
     '';
   };
 
@@ -18,6 +19,9 @@ with lib;
     # mullvad-daemon writes to /etc/iproute2/rt_tables
     networking.iproute2.enable = true;
 
+    # See https://github.com/NixOS/nixpkgs/issues/113589
+    networking.firewall.checkReversePath = "loose";
+
     systemd.services.mullvad-daemon = {
       description = "Mullvad VPN daemon";
       wantedBy = [ "multi-user.target" ];
@@ -42,5 +46,5 @@ with lib;
     };
   };
 
-  meta.maintainers = [ maintainers.xfix ];
+  meta.maintainers = with maintainers; [ ymarkus ];
 }