opengl: DMABuf export fix
This contains few fixes for DMABuf exportation path.
- Wait on sync meta if any, with DMABuf we won't be on sync otherwise, which caused tearing.
- Prevent the export path from being used when the exported DMABuf would require a modifier.
- Fix exported DMABuf size
- Fix bad extension name check
- Re-factored selection of the download mode
- Fix renegotiation per frame when DMABuf export fails
Edited by Nicolas Dufresne