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

api/system-current.txt

@@ -6061,7 +6061,7 @@ package android.net {
     method public void release();
   }
 
-  public class InvalidPacketException extends java.lang.Exception {
+  public final class InvalidPacketException extends java.lang.Exception {
     ctor public InvalidPacketException(int);
     method public int getError();
     field public static final int ERROR_INVALID_IP_ADDRESS = -21; // 0xffffffeb
@@ -6255,7 +6255,7 @@ package android.net {
     field public static final int NET_CAPABILITY_PARTIAL_CONNECTIVITY = 24; // 0x18
   }
 
-  public static class NetworkCapabilities.Builder {
+  public static final class NetworkCapabilities.Builder {
     ctor public NetworkCapabilities.Builder();
     ctor public NetworkCapabilities.Builder(@NonNull android.net.NetworkCapabilities);
     method @NonNull public android.net.NetworkCapabilities.Builder addCapability(int);

api/test-current.txt

@@ -1833,7 +1833,7 @@ package android.net {
     field public static final int TRANSPORT_TEST = 7; // 0x7
   }
 
-  public static class NetworkCapabilities.Builder {
+  public static final class NetworkCapabilities.Builder {
     ctor public NetworkCapabilities.Builder();
     ctor public NetworkCapabilities.Builder(@NonNull android.net.NetworkCapabilities);
     method @NonNull public android.net.NetworkCapabilities.Builder addCapability(int);

core/java/android/net/InvalidPacketException.java

@@ -27,7 +27,7 @@ import java.lang.annotation.RetentionPolicy;
  * @hide
  */
 @SystemApi
-public class InvalidPacketException extends Exception {
+public final class InvalidPacketException extends Exception {
     private final int mError;
 
     // Must match SocketKeepalive#ERROR_INVALID_IP_ADDRESS.

core/java/android/net/NetworkCapabilities.java

@@ -2000,7 +2000,7 @@ public final class NetworkCapabilities implements Parcelable {
      */
     @SystemApi
     @TestApi
-    public static class Builder {
+    public static final class Builder {
         private final NetworkCapabilities mCaps;
 
         /**