glx/dri2: rework __DRIextension handling

Make sure that the DRI*Extensions report the version of the interface
implemented over the listed in the headers. While both are currently
the same, this may change in the future.

v2: Keep loader extensions handling as is.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> (v1)
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>

src/glx/dri2_glx.c

@@ -969,7 +969,7 @@ static const __DRIdri2LoaderExtension dri2LoaderExtension_old = {
 };
 
 static const __DRIuseInvalidateExtension dri2UseInvalidate = {
-   { __DRI_USE_INVALIDATE, __DRI_USE_INVALIDATE_VERSION }
+   .base = { __DRI_USE_INVALIDATE, 1 }
 };
 
 _X_HIDDEN void