osmesa: use _mesa_generate_mipmap() for mipmap generation, not meta

See previous commit for more info.

Note: This is a candidate for the 9.0 branch.

Reviewed-by: José Fonseca <jfonseca@vmware.com>
(cherry picked from commit 2180f32972)

src/mesa/drivers/osmesa/osmesa.c

@@ -42,6 +42,7 @@
 #include "main/framebuffer.h"
 #include "main/imports.h"
 #include "main/macros.h"
+#include "main/mipmap.h"
 #include "main/mtypes.h"
 #include "main/renderbuffer.h"
 #include "main/version.h"
@@ -783,6 +784,8 @@ OSMesaCreateContextExt( GLenum format, GLint depthBits, GLint stencilBits,
          ctx->Driver.MapRenderbuffer = osmesa_MapRenderbuffer;
          ctx->Driver.UnmapRenderbuffer = osmesa_UnmapRenderbuffer;
 
+         ctx->Driver.GenerateMipmap = _mesa_generate_mipmap;
+
          /* Extend the software rasterizer with our optimized line and triangle
           * drawing functions.
           */