API review: make exception class and Builder final

- InvalidPacketException exception class should be final
- NetworkCapabilities.Builder should be final

Bug: 152203926
Test: atest FrameworksNetTests
Change-Id: If9b799151aff6d41c9bcd8bb86c65a58e46bad73
diff --git a/core/java/android/net/InvalidPacketException.java b/core/java/android/net/InvalidPacketException.java
index b3b0f11..1873d77 100644
--- a/core/java/android/net/InvalidPacketException.java
+++ b/core/java/android/net/InvalidPacketException.java
@@ -27,7 +27,7 @@
  * @hide
  */
 @SystemApi
-public class InvalidPacketException extends Exception {
+public final class InvalidPacketException extends Exception {
     private final int mError;
 
     // Must match SocketKeepalive#ERROR_INVALID_IP_ADDRESS.
diff --git a/core/java/android/net/NetworkCapabilities.java b/core/java/android/net/NetworkCapabilities.java
index fcfcebd..05d7860 100644
--- a/core/java/android/net/NetworkCapabilities.java
+++ b/core/java/android/net/NetworkCapabilities.java
@@ -2000,7 +2000,7 @@
      */
     @SystemApi
     @TestApi
-    public static class Builder {
+    public static final class Builder {
         private final NetworkCapabilities mCaps;
 
         /**