Update VPN isolation code for excluded routes

Bug: 230058738
Test: atest LinkPropertiesTest

Result: https://paste.googleplex.com/4706859672928256

Change-Id: I970fca6b0e2cd358e9bd77152563d13367867c74

framework/src/android/net/LinkProperties.java

@@ -1365,6 +1365,21 @@ public final class LinkProperties implements Parcelable {
         return false;
     }
 
+    /**
+     * Returns true if this link has a throw route.
+     *
+     * @return {@code true} if there is an exclude route, {@code false} otherwise.
+     * @hide
+     */
+    public boolean hasExcludeRoute() {
+        for (RouteInfo r : mRoutes) {
+            if (r.getType() == RouteInfo.RTN_THROW) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * Compares this {@code LinkProperties} interface name against the target
      *