Expose SocketKeepalive#SUCCESS as SystemApi

Support wifi mainline module usage.

Bug: 135998869
Test: Build and make system-api-stubs-docs-update-current-api
      atest FrameworksNetTests
Change-Id: I94171b2dc4f26442df918547bf8bc40953f63f2e
Merged-In: I94171b2dc4f26442df918547bf8bc40953f63f2e
diff --git a/api/system-current.txt b/api/system-current.txt
index 73bfd20..a974044 100755
--- a/api/system-current.txt
+++ b/api/system-current.txt
@@ -4567,6 +4567,10 @@
     field public final android.net.RssiCurve rssiCurve;
   }
 
+  public abstract class SocketKeepalive implements java.lang.AutoCloseable {
+    field public static final int SUCCESS = 0; // 0x0
+  }
+
   public final class StaticIpConfiguration implements android.os.Parcelable {
     ctor public StaticIpConfiguration();
     ctor public StaticIpConfiguration(@Nullable android.net.StaticIpConfiguration);
diff --git a/core/java/android/net/SocketKeepalive.java b/core/java/android/net/SocketKeepalive.java
index fb224fb..fc9a8f6 100644
--- a/core/java/android/net/SocketKeepalive.java
+++ b/core/java/android/net/SocketKeepalive.java
@@ -20,6 +20,7 @@
 import android.annotation.IntRange;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
+import android.annotation.SystemApi;
 import android.os.Binder;
 import android.os.ParcelFileDescriptor;
 import android.os.RemoteException;
@@ -53,7 +54,11 @@
 public abstract class SocketKeepalive implements AutoCloseable {
     static final String TAG = "SocketKeepalive";
 
-    /** @hide */
+    /**
+     * No errors.
+     * @hide
+     */
+    @SystemApi
     public static final int SUCCESS = 0;
 
     /** @hide */