Add static fallback IP address

[schmidma]

When something fails during the setup of the network devices of the NAO (e.g. wrong syntax in team.toml or missing Head-ID), the robot is not reachable via network, and one has to open the head and plug in a cable for the serial console.

We should add a static fallback in some private IP address range (https://en.wikipedia.org/wiki/Private_network#Private_IPv4_addresses) instead of just doing DHCP.