Fix ddclient extraConfig

The the extraConfig variable is added below the domain variable in the
ddclient config file. The domain variable should always be last.

(cherry picked from commit ba0ba6dc7934a6b4cc5d4090739a3a1c839afe67)

nixos/modules/services/networking/ddclient.nix

@@ -20,8 +20,8 @@ let
     wildcard=YES
     quiet=${boolToStr cfg.quiet}
     verbose=${boolToStr cfg.verbose}
-    ${lib.concatStringsSep "," cfg.domains}
     ${cfg.extraConfig}
+    ${lib.concatStringsSep "," cfg.domains}
   '';
 
 in