The structure of the controllers is really similar to addresses and
routes:
* `LinkSpec` resource describes desired link state
* `LinkConfig` controller generates `LinkSpecs` based on machine
configuration and kernel cmdline
* `LinkMerge` controller merges multiple configuration sources into a
single `LinkSpec` paying attention to the config layer priority
* `LinkSpec` controller applies the specs to the kernel state
Controller `LinkStatus` (which was implemented before) watches the
kernel state and publishes current link status.
Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>
