Add more context in javadoc of setDataSaverEnabled

This addresses API council review feedback at b/307695368

Test: TH
Fix: 307695368
Change-Id: Ifc8cb890ff73be423d38e06a516853da4b9ee97f
diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index fa27d0e..1ea1815 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -6022,6 +6022,13 @@
     /**
      * Sets data saver switch.
      *
+     * <p>This API configures the bandwidth control, and filling data saver status in BpfMap,
+     * which is intended for internal use by the network stack to optimize performance
+     * when frequently checking data saver status for multiple uids without doing IPC.
+     * It does not directly control the global data saver mode that users manage in settings.
+     * To query the comprehensive data saver status for a specific UID, including allowlist
+     * considerations, use {@link #getRestrictBackgroundStatus}.
+     *
      * @param enable True if enable.
      * @throws IllegalStateException if failed.
      * @hide