[SB] Update ethernet icon datasource to be EthernetInteractor.

This is the last piece needed to completely remove SignalCallback usage
from StatusBarSignalPolicy.

Bug: 291321279
Flag: com.android.systemui.status_bar_signal_policy_refactor_ethernet
Test: connect and disconnect from ethernet -> verify status bar icon
appears and disappears correctly
Test: atest StatusBarSignalPolicyTest

Change-Id: I140ddc35e65fce63f6770f7c576ee7d11c7f2c51