Marking eth network management APIs @SystemApi

Annotating ethernet network management APIs in EthernetManager
with @SystemApi.

Bug: 210485380
Test: atest EthernetServiceTests
atest CtsNetTestCasesLatestSdk

Change-Id: I10429441fd4d7b9bcaa7437b844420a43a415d72
Merged-In: I10429441fd4d7b9bcaa7437b844420a43a415d72
4 files changed