Marking eth network management APIs @SystemApi

Annotating ethernet network management APIs in EthernetManager
with @SystemApi.

Bug: 210485380
Test: atest EthernetServiceTests
      atest CtsNetTestCasesLatestSdk

cherry pick of aosp/1969839

Change-Id: I10429441fd4d7b9bcaa7437b844420a43a415d72
3 files changed
tree: fbe20affa2557c1183c58fd7716c87a737cb67ee
  1. framework/
  2. framework-t/
  3. service-t/
  4. services/
  5. tests/