nanny: Introduce ni_nanny_policy_load()
fsm: Do not print state info on success
nannny: Reset ifworker when policy exists
ifup: Return ifstatus on AddressAcquire
nanny: Introduce ni_nanny_policy_drop()

Policy is being dropped on:
- disable() method call
- DEVICE_DELETE event
ifup: Handle ifstatus with biref option
ifdown: Enable firing nanny again