Make isHostRoute match only host routes

Currently, isHostRoute returns true iff the gateway address is
the unspecified address (0.0.0.0 or ::). Thus, it will return
true for any route that has no gateway (e.g., a route pointing at
a point-to-point interface), even if the route is not a host
route.

Fix this by checking the prefix length instead. This should be
safe because:

1. mDestination cannot be null, since it's created using new.
2. Host routes created using makeHostRoute (which is what
   ConnectivityService calls) always have the correct prefix
   lengths (/32 or /128) set.

Bug: 8276725
Change-Id: I14285398823fa6c312349128c7cc216cad4a84c9

core/java/android/net/RouteInfo.java

@@ -132,7 +132,10 @@ public class RouteInfo implements Parcelable {
     }
 
     private boolean isHost() {
-        return (mGateway.equals(Inet4Address.ANY) || mGateway.equals(Inet6Address.ANY));
+        return (mDestination.getAddress() instanceof Inet4Address &&
+                mDestination.getNetworkPrefixLength() == 32) ||
+               (mDestination.getAddress() instanceof Inet6Address &&
+                mDestination.getNetworkPrefixLength() == 128);
     }
 
     private boolean isDefault() {