How to get Android connected to the Internet through sl0 (slip, serial line Internet protocol)

i want to connect my Android device to the Internet via a serial line (the serial line will be a point to point air link later, but for first Tests i'm just using two connected FTDIs).

What i've done so far is testing the slip link with two Linux machines, that are connected together via two FTDIs and one oft them forwards the Internet traffic of the other one. This works flawlessly.

AS next step i've build a custom kernel with the ftdi-sio module, installed busybox and configured the slip link like before on the Linux machines. Ping with IPs works and nslookup with a hostname also works as root, but not as normal user. Routing table of Route command is configured to be the same as before.

My question now is how to tell Android to use the New slip link sl0 for Internet connection for normal user.

Kind regards