Use the proper IpPrefix and LinkAddress constructors in VPN code.

This simplifies the code, and also makes it possible for
users to point multicast routes at the VPN. The LinkAddress
objects we were previously using to construct the RouteInfo do
not accept these, but IpPrefix objects do.

Bug: 18485968
Change-Id: Ie914a2eb359b78161810ee473df725059f944f4e
diff --git a/core/java/android/net/VpnService.java b/core/java/android/net/VpnService.java
index f6b6978..c26af06 100644
--- a/core/java/android/net/VpnService.java
+++ b/core/java/android/net/VpnService.java
@@ -501,7 +501,7 @@
                     }
                 }
             }
-            mRoutes.add(new RouteInfo(new LinkAddress(address, prefixLength), null));
+            mRoutes.add(new RouteInfo(new IpPrefix(address, prefixLength), null));
             mConfig.updateAllowedFamilies(address);
             return this;
         }