qt: use static free functions for C callbacks

Callbacks to be called from C should be free functions rather than class
members.

modules/gui/qt/network/networksourcelistener.cpp

 #include "networksourcelistener.hpp"
 
-NetworkSourceListener::NetworkSourceListener(MediaSourcePtr s, SourceListenerCb* m)
-    : source( s )
-    , listener( nullptr, [s]( vlc_media_tree_listener_id* l ) {
-            vlc_media_tree_RemoveListener( s->tree, l );
-        } )
-    , cb( m )
-{
-    static const vlc_media_tree_callbacks cbs {
-        &NetworkSourceListener::onItemCleared,
-        &NetworkSourceListener::onItemAdded,
-        &NetworkSourceListener::onItemRemoved,
-        &NetworkSourceListener::onItemPreparseEnded
-    };
-    auto l = vlc_media_tree_AddListener( s->tree, &cbs, this, true );
-    if ( l == nullptr )
-        return;
-    listener.reset( l );
-}
-
-void NetworkSourceListener::onItemCleared( vlc_media_tree_t*, input_item_node_t* node,
-                                                    void* userdata)
+static void onItemCleared(vlc_media_tree_t*, input_item_node_t *node,
+                          void* userdata)
 {
     auto* self = static_cast<NetworkSourceListener*>( userdata );
     self->cb->onItemCleared( self->source, node );
 }
 
-void NetworkSourceListener::onItemAdded( vlc_media_tree_t *, input_item_node_t * parent,
-                                  input_item_node_t *const children[], size_t count,
-                                  void *userdata )
+static void onItemAdded(vlc_media_tree_t *, input_item_node_t *parent,
+                        input_item_node_t *const children[], size_t count,
+                        void *userdata)
 {
     auto* self = static_cast<NetworkSourceListener*>( userdata );
     auto source = self->source;
     self->cb->onItemAdded( self->source, parent, children, count );
 }
 
-void NetworkSourceListener::onItemRemoved( vlc_media_tree_t *, input_item_node_t * node,
-                                    input_item_node_t *const children[], size_t count,
-                                    void *userdata )
+static void onItemRemoved(vlc_media_tree_t *, input_item_node_t *node,
+                          input_item_node_t *const children[], size_t count,
+                          void *userdata)
 {
     auto* self = static_cast<NetworkSourceListener*>( userdata );
     self->cb->onItemRemoved( self->source, node, children, count );
 }
 
-void NetworkSourceListener::onItemPreparseEnded(vlc_media_tree_t *, input_item_node_t * node, enum input_item_preparse_status status, void *userdata)
+static void onItemPreparseEnded(vlc_media_tree_t *, input_item_node_t * node,
+                                enum input_item_preparse_status status,
+                                void *userdata)
 {
     auto* self = static_cast<NetworkSourceListener*>( userdata );
     self->cb->onItemPreparseEnded( self->source, node, status );
 }
+
+NetworkSourceListener::NetworkSourceListener(MediaSourcePtr s, SourceListenerCb* m)
+    : source( s )
+    , listener( nullptr, [s]( vlc_media_tree_listener_id* l ) {
+            vlc_media_tree_RemoveListener( s->tree, l );
+        } )
+    , cb( m )
+{
+    static const vlc_media_tree_callbacks cbs {
+        &onItemCleared,
+        &onItemAdded,
+        &onItemRemoved,
+        &onItemPreparseEnded
+    };
+    auto l = vlc_media_tree_AddListener( s->tree, &cbs, this, true );
+    if ( l == nullptr )
+        return;
+    listener.reset( l );
+}

modules/gui/qt/network/networksourcelistener.hpp

@@ -58,19 +58,6 @@ public:
     NetworkSourceListener( const NetworkSourceListener& ) = delete;
     NetworkSourceListener& operator=( const NetworkSourceListener& ) = delete;
 
-    static void onItemCleared( vlc_media_tree_t* tree, input_item_node_t* node,
-                               void* userdata );
-    static void onItemAdded( vlc_media_tree_t *tree, input_item_node_t *node,
-                             input_item_node_t *const children[], size_t count,
-                             void *userdata );
-    static void onItemRemoved( vlc_media_tree_t *tree, input_item_node_t *node,
-                               input_item_node_t *const children[], size_t count,
-                               void *userdata );
-
-    static void onItemPreparseEnded( vlc_media_tree_t *tree, input_item_node_t *node,
-                                     enum input_item_preparse_status status,
-                                     void *userdata );
-
     MediaSourcePtr source;
     ListenerPtr listener = nullptr;
     SourceListenerCb *cb = nullptr;