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

This reverts commit 758ead6dd3.

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

Change-Id: I2f705549d85af4ba45dc294e0a86d757490b1cd7

tests/common/java/android/net/IpPrefixTest.java

@@ -122,6 +122,9 @@ public class IpPrefixTest {
 
         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