Well that sucks.Look here:
https://code.google.com/p/quake-gamecube/source/browse/trunk/quake-wii/src/wii/net_udp_wii.c?r=216
The filename says "NET_UDP_WII". It's from the Quake port to the Wii but as said: no SDL after all.
Hope someone with more knowledge than me can help out.
I'll still be on the lookout for SDL UDP eitherway
Out of curiosity:
What are you trying to accomplish by implementing network features into your ports?