No longer ignore Linux virtual interfaces. Fixes redmine #1490, #3420

This fixes red mine bugs [#1490][rm1490] and [#3420][rm3420].

Regarding [this help-cfengine discussion about missing interfaces][hcf], and [Mark's comment][note-14] that there's no longer any reason to keep this.

[note-14]: https://dev.cfengine.com/issues/1490#note-14
[hcf]: https://groups.google.com/forum/m/#!topic/help-cfengine/3jEu9Jc3wek
[rm1490]: https://dev.cfengine.com/issues/1490
[rm3420]: https://dev.cfengine.com/issues/3420