Add a class lable parameter to idletimer.

Now the idletimer should be setup by this command:
ndc idletimer add <interface> <timeout> <class label>

Class label can be a number or string to identify device type, such as
mobile or wifi. Idletimer will send label in the netd message instead
of the actual interface name.

Change-Id: Ic8b69dc5e38a4436c74723697905643a1214aa2a
7 files changed