Fix advertising timers

Right now, timers that rotate advertising address are started when stack
is starting and keep running all the time even when advertising is not
used. This patch fix that by starting the timer when advertising
instance is registered, and stopping it when it's unregistered.

Bug: 30622771
Change-Id: I638176bdc2f26c62d5ec3a56f6e81cd9c016df0b