Bug 624546 – Modification of GDBusMessage in filter function

Rework filter functions as per

 https://bugzilla.gnome.org/show_bug.cgi?id=624546#c8

This commit breaks ABI. However, this ABI break affects only
applications using filter functions. The only known user of is dconf.

Signed-off-by: David Zeuthen <davidz@redhat.com>

gio/tests/gdbus-peer.c

@@ -1313,7 +1313,7 @@ test_credentials (void)
 #define OVERFLOW_NUM_SIGNALS 5000
 #define OVERFLOW_TIMEOUT_SEC 10
 
-static GDBusMessageFilterResult
+static GDBusMessage *
 overflow_filter_func (GDBusConnection *connection,
                       GDBusMessage    *message,
                       gboolean         incoming,
@@ -1321,7 +1321,7 @@ overflow_filter_func (GDBusConnection *connection,
 {
   volatile gint *counter = user_data;
   *counter += 1;
-  return G_DBUS_MESSAGE_FILTER_RESULT_NO_EFFECT;
+  return message;
 }
 
 static gboolean