Fixes for LLADDR="00:00:00:00:00:00"

Should address at least: bnc#889287, bnc#898620


this is not good idea how to test it, as include expect shortcuts from Yast module. So better, robust and more safe way is:
```
class NetworkLanS390IncludeTest < Yast::Module
  include Singleton
  def initialize
    Yast.include self, "network/lan/s390.rb"
  end
end
```