Add NetworkStackConstants to framework/

The constants are also useful for bootclasspath code, for example in
Ikev2VpnProfile.

Bug: 174436414
Test: atest FrameworksNetTests NetworkStackTests NetworkStaticLibTests
Change-Id: I34458fe6568a73533f956f86ed7bb50d45aa7d7e
diff --git a/staticlibs/device/com/android/net/module/util/NetworkStackConstants.java b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
similarity index 99%
rename from staticlibs/device/com/android/net/module/util/NetworkStackConstants.java
rename to staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
index 1088477..1572fe0 100644
--- a/staticlibs/device/com/android/net/module/util/NetworkStackConstants.java
+++ b/staticlibs/framework/com/android/net/module/util/NetworkStackConstants.java
@@ -22,6 +22,7 @@
 
 /**
  * Network constants used by the network stack.
+ * @hide
  */
 public final class NetworkStackConstants {