Add additional option support

In RedHat there are many more options that can be specified after the interface. For example, you can specify a routing table such as `default via 10.0.0.1 dev eth1 table 200`. Everything after the interface is so fluid it doesn't make sense to add specific properties for everything. A simple `additional_options` property is most flexible.

I don't know what or if any additional options are available in Debian but I added support anyway. It certainly shouldn't hurt. If someone else can test the Debian side to see if it's needed that'd be great.

Please let me know if you have any questions.