ethernet: report server mode interfaces when listener is registered

When a new InterfaceStateListener is registered, server mode interfaces
were not properly reported. This is a bug that affects Tethering
settings.

This fix does not affect any existing callbacks.

Bug: 236895792
Bug: 269004812
Test: atest EthernetManagerTest
Change-Id: Ie102f96239bbc555b6ed42f5c4e7ed251547d96f