Add Nat64Prefix to LinkProperties copy constructor

The attribute is copied when parceling/unparceling so should also be
preserved in the copy constructor.

Test: tests based on this pass
Change-Id: Ia48d94fc075e6414f537dad181a236be5a32b41b
diff --git a/core/java/android/net/LinkProperties.java b/core/java/android/net/LinkProperties.java
index 617125b3..c2963fd 100644
--- a/core/java/android/net/LinkProperties.java
+++ b/core/java/android/net/LinkProperties.java
@@ -191,6 +191,7 @@
             }
             setMtu(source.mMtu);
             mTcpBufferSizes = source.mTcpBufferSizes;
+            mNat64Prefix = source.mNat64Prefix;
         }
     }