Refactor LLDP form to new ix-forms

We have several ways of working with forms in our system: entity-forms and ix-forms. Entity forms is an older configuration-based design that we want to transition from, while ix-forms is a more Angular-like approach.

TODO: Refactor form in System Settings -> Services -> LLDP. See ServiceLLDPComponent.

Notes:

See ServiceSshComponent and ServiceSmartComponent for an example of how to do forms with ix-forms.
Remove unused code in ServiceLLDPComponent if any.
Update code style to our code style (for example ServiceLLDPComponent => ServiceLldpComponent)
Add unit tests.
Remember about error handling, translations and loading indicators.
There is a custom countryValidator. See if needs to be extracted somewhere. Also see ix-errors and IxValidatorsService for an example on how to work with errors.