Revert "Revert "Unhide IpPrefix(InetAddress, int)""

This reverts commit 758ead6dd362f8b7c665603fb9d85038b3f72f27.

Reason for revert: Re-landing changes not related to postsubmit failure

Change-Id: I2f705549d85af4ba45dc294e0a86d757490b1cd7
diff --git a/tests/common/java/android/net/IpPrefixTest.java b/tests/common/java/android/net/IpPrefixTest.java
index 50ecb42..f61c8c3 100644
--- a/tests/common/java/android/net/IpPrefixTest.java
+++ b/tests/common/java/android/net/IpPrefixTest.java
@@ -122,6 +122,9 @@
 
         p = new IpPrefix("[2001:db8::123]/64");
         assertEquals("2001:db8::/64", p.toString());
+
+        p = new IpPrefix(InetAddresses.parseNumericAddress("::128"), 64);
+        assertEquals("::/64", p.toString());
     }
 
     @Test