TT#105151 Allow interfaces to be named either "eth*" or "neth*"

This could be restricted this in the future to only "neth*" or others if
we settle on that, but at the moment keep it a bit flexible while we're
migrating and make things easier if we have to step back and look again.

Change-Id: Id96970ed0dfdd3bae59120ae19a35bd2523d1294

templates/830_network-interfaces-legacy.yaml.tt2

@@ -12,5 +12,5 @@ command:
 
   ip link:
     exit-status: 0
-    stdout: ['/: eth[0-9]/']
+    stdout: ['/: n?eth[0-9]/']
     stderr: []