DE2-115 Ethernet not working

I didn't look at the code in detail, but it doesn't look like a complete TCP/IP stack. That demo just shows basic passing of data from one Ethernet port to the other. The initializing code is for loop back, not passing packets through. Look at driver code for other boards that use this phy chip as an example of how to set it up. Note that different phy chips were used on the DE series boards, depending on how old they are. Make sure the code you are using matches the phy chip, and that it is for communication not just loop back testing.