This includes multiple controllers responsible for different stages of
`AddressSpec` conversion:
* `AddressConfigController` produces initial unmerged configuration from
multiple sources (more sources coming later, e.g. DHCP)
* `AddressMergeController` merges address configuration into final
representation
* `AddressSpecController` syncs resources with kernel state
Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>
