qio: Prepare NetListener to use AioContext

For ease of review, this patch adds an AioContext pointer to the
QIONetListener struct, the code to trace it, and refactors
listener->io_source to instead be an array of utility structs; but the
aio_context pointer is always NULL until the next patch adds an API to
set it.  There should be no semantic change in this patch.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20251113011625.878876-25-eblake@redhat.com>

include/io/net-listener.h

@@ -28,6 +28,7 @@
 OBJECT_DECLARE_SIMPLE_TYPE(QIONetListener,
                            QIO_NET_LISTENER)
 
+typedef struct QIONetListenerSource QIONetListenerSource;
 
 typedef void (*QIONetListenerClientFunc)(QIONetListener *listener,
                                          QIOChannelSocket *sioc,
@@ -47,10 +48,11 @@ struct QIONetListener {
     Object parent;
 
     char *name;
-    QIOChannelSocket **sioc;
-    GSource **io_source;
+    QIONetListenerSource **source;
     size_t nsioc;
+    /* At most one of context or aio_context will be set */
     GMainContext *context;
+    AioContext *aio_context;
 
     bool connected;