Add NETWORK_SETTINGS to SystemApi

The permissions are checked by Tethering; mainline modules should be
able to do permission checks based on these permissions.

Bug: 135411507
Test: m
Test: make test-api-stubs-docs-update-current-api \
      system-api-stubs-docs-update-current-api

Change-Id: Ia617ea56aba18f98371d7dbd546679e0327bfacd

api/test-current.txt

@@ -15,6 +15,7 @@ package android {
     field public static final String MANAGE_ACTIVITY_STACKS = "android.permission.MANAGE_ACTIVITY_STACKS";
     field public static final String MANAGE_CRATES = "android.permission.MANAGE_CRATES";
     field public static final String MANAGE_ROLLBACKS = "android.permission.MANAGE_ROLLBACKS";
+    field public static final String NETWORK_SETTINGS = "android.permission.NETWORK_SETTINGS";
     field public static final String NETWORK_STACK = "android.permission.NETWORK_STACK";
     field public static final String READ_CELL_BROADCASTS = "android.permission.READ_CELL_BROADCASTS";
     field public static final String REMOVE_TASKS = "android.permission.REMOVE_TASKS";

core/res/AndroidManifest.xml

@@ -1656,7 +1656,7 @@
 
     <!-- Allows Settings and SystemUI to call methods in Networking services
          <p>Not for use by third-party or privileged applications.
-         @SystemApi
+         @SystemApi @TestApi
          @hide This should only be used by Settings and SystemUI.
     -->
     <permission android:name="android.permission.NETWORK_SETTINGS"