gst: pool: Some refinements to min/max handling

A number of changes for correctness.

  1) We expose the actualy min and max values we support in the
     allocation query.

  2) We don't support max_buffers as 0, as unlimited buffers is not an
     option

  3) In ParamBuffers, we request the max_buffers from bufferpool config,
     as we cannot dynamically allocate buffers

src/gst/gstpipewirepool.h

@@ -18,6 +18,9 @@ G_BEGIN_DECLS
 #define GST_TYPE_PIPEWIRE_POOL (gst_pipewire_pool_get_type())
 G_DECLARE_FINAL_TYPE (GstPipeWirePool, gst_pipewire_pool, GST, PIPEWIRE_POOL, GstBufferPool)
 
+#define PIPEWIRE_POOL_MIN_BUFFERS 2u
+#define PIPEWIRE_POOL_MAX_BUFFERS 16u
+
 typedef struct _GstPipeWirePoolData GstPipeWirePoolData;
 struct _GstPipeWirePoolData {
   GstPipeWirePool *pool;