Allow to configure asymmetric links

[OlegHahm]

Most of the links wireless networks are asymmetric, but all configured links in desvirt are symmetric by default.

[cgundogan]

can be closed AFAIK this option is already supported

[mfrey]

could you please verify before you suggest to close it?

[cgundogan]

Maybe I didn't understand it correctly, but isn't it possible to specify links with uni=true to be unidirectional? And every link has its own loss rate .. so I assumed that this would fit to what @OlegHahm was pointing at.