Title: Fixed rare Bug in case of clusterd network interfaces
Level: 1
Component: checks
Class: fix
Compatible: compat
State: unknown
Version: 1.2.7i1
Date: 1425041662

In case that all network interfaces don't have traffic for a moment (or counter wraps), Check_MK was unable to determine the active one.
The only solution is to use a random one here. 
