nixos/epmd: allow setting multiple listen addresses

In some contexts, for example systems with net.ipv6.bindv6only turned
on, it is desirable to set multiple addresses to listen on. The systemd
unit option already allows this, so just expose it on the module.

nixos/modules/services/networking/epmd.nix

@@ -5,6 +5,8 @@
   ...
 }:
 let
+  inherit (lib.types) listOf oneOf str;
+
   cfg = config.services.epmd;
 in
 {
@@ -21,7 +23,10 @@ in
     };
     package = lib.mkPackageOption pkgs "erlang" { };
     listenStream = lib.mkOption {
-      type = lib.types.str;
+      type = oneOf [
+        str
+        (listOf str)
+      ];
       default = "[::]:4369";
       description = ''
         the listenStream used by the systemd socket.