Check your cable. the most likely culprit when you're getting packet loss like this on a wired connection is something wrong with the connection medium. You might want to:
- Swap out the cable for a known good one and see if it works
- Ensure that the cable is seated correctly in its plugs on both ends
- Check for any sources of electrical noise. The cable is supposedly shielded, but something like having it wrapped around your DS's adapter might still hurt your connection quality.