Fix build of trunk with gcc-16 (deadbeef DDB_API_LEVEL >= 11 / >= 17).

The two waveform.c fixes from deadbeef-waveform-seekbar-gcc16.patch, with
trunk's context, plus one trunk-only diagnostic gcc-16 now treats as a
hard error:
  * ddb_waveformat_t.is_bigendian was replaced by `flags` at
    DDB_API_LEVEL 17; drop the initializer, which set the default anyway.
  * the action callback used the pre-API-11 `int ctx` signature;
    DB_plugin_action_callback2_t now takes ddb_action_context_t.
  * config_dialog.c (reworked after 0.5) passes the GtkMenuItem to
    gtk_widget_get_toplevel() and its GtkWidget result to
    gtk_window_set_transient_for(); cast both.

Upstream inactive since 2022; carried locally.
--- a/config_dialog.c
+++ b/config_dialog.c
@@ -79,7 +79,7 @@
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
     waveform_properties = gtk_dialog_new ();
-    gtk_window_set_transient_for (GTK_WINDOW (waveform_properties), gtk_widget_get_toplevel(menuitem));
+    gtk_window_set_transient_for (GTK_WINDOW (waveform_properties), GTK_WINDOW (gtk_widget_get_toplevel (GTK_WIDGET (menuitem))));
     gtk_window_set_title (GTK_WINDOW (waveform_properties), "Waveform Properties");
     gtk_window_set_type_hint (GTK_WINDOW (waveform_properties), GDK_WINDOW_TYPE_HINT_DIALOG);
 
--- a/waveform.c
+++ b/waveform.c
@@ -687,7 +687,6 @@
                 .samplerate = fileinfo->fmt.samplerate,
                 .channelmask = fileinfo->fmt.channelmask,
                 .is_float = 1,
-                .is_bigendian = 0
             };
 
             int update_counter = 0;
@@ -1369,7 +1368,7 @@
 }
 
 static int
-waveform_action_lookup (DB_plugin_action_t *action, int ctx)
+waveform_action_lookup (DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     DB_playItem_t *it = NULL;
     deadbeef->pl_lock ();