In commit edd1295e1d I've introduced an
XML element that allows to configure state of the network interface
link. Somehow the RNG schema hunk ended up in a weird place in the
network schema definition. Move it to the right place and add a test
case.
Note that the link state is set up via the monitor at VM startup so I
originally didn't think of adding a test case.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1173468