Zeroconf configuration fails if 192.0.2.0 is unreachable

[TobiasSchaffner]

zeroconf.ServiceInfo expect the IP address that should be announced by zeroconfig as argument. This should be the IP address of the external interface.

At the moment a 'hack' is used to determine the IP address. A socket is opened to a hardcoded address and the local ip of this socket is used. https://github.com/siemens/mtda/blame/aecc0f725577600433c4d8c1aafefd74137747a5/mtda-service#L61

This fails if the hardcoded address is unreachable.