Annotate @SystemApi with required permissions.

Most @SystemApi methods should be protected with system (or higher)
permissions, so annotate common methods with @RequiresPermission to
make automatic verification easier.

Verification is really only relevant when calling into system
services (where permissions checking can happen on the other side of
a Binder call), so annotate managers with the new @SystemService
annotation, which is now automatically documented.

This is purely a docs change; no logic changes are being made.

Test: make -j32 update-api && make -j32 offline-sdk-docs
Bug: 62263906
Change-Id: I2554227202d84465676aa4ab0dd336b5c45fc651

core/java/android/net/EthernetManager.java

@@ -16,6 +16,7 @@
 
 package android.net;
 
+import android.annotation.SystemService;
 import android.content.Context;
 import android.net.IEthernetManager;
 import android.net.IEthernetServiceListener;
@@ -31,6 +32,7 @@ import java.util.ArrayList;
  *
  * @hide
  */
+@SystemService(Context.ETHERNET_SERVICE)
 public class EthernetManager {
     private static final String TAG = "EthernetManager";
     private static final int MSG_AVAILABILITY_CHANGED = 1000;