feat: More updates to the Ethernet interface Layer3 spec (#138)

* feat: More updates to the Ethernet interface spec

* Change ethernet.yaml layer3 ip address to object

When sdwan-link-settings is enabled, ip entry gains an
additional optiona parameter, sdwan-next-hop.

* Add sdwan-related layer3 configuration

* More changes to ethernet interface spec

* Add layer3 arp and fix layer3 lldp