(Copied and pasted from IFIXIT- the link didn't show the 'solution' which I thought might be confusing, so I opened it and just pasted that)
Posted: 12/02/2009
I found a very simple fix to the "restart after sleep" problem on the Apple user forum.
1. In System Preferences, open Network preferences.
2. Highlight "Ethernet" or "Built in Ethernet".
3. Click the Minus sign ( - ) (at the bottom of the window just above the unlocked lock icon) to delete the Ethernet configuration.
4. Click the Plus sign ( + ) (at the bottom of the window just above the lock icon) then select "Ethernet" from the menu that appears. Then click "CREATE". (a new Ethernet configuration is created in the left section of the window). Then click "APPLY" on the lower right side of the window.