Remove hidden method link in public addRoute API

The build will complain after moving connectivity framework code
outside framework because the hidden methods/members accesses are
not allowed anymore. Link to a hidden class will not work since
it's not visible in public.

Bug: 182859030
Test: make docs
Change-Id: I5726f80be7cf92b648ce851d9601d5f58bc2b647
diff --git a/framework/src/android/net/LinkProperties.java b/framework/src/android/net/LinkProperties.java
index e41ed72..99f48b4 100644
--- a/framework/src/android/net/LinkProperties.java
+++ b/framework/src/android/net/LinkProperties.java
@@ -686,8 +686,8 @@
     }
 
     /**
-     * Adds a {@link RouteInfo} to this {@code LinkProperties}, if a {@link RouteInfo}
-     * with the same {@link RouteInfo.RouteKey} with different properties
+     * Adds a {@link RouteInfo} to this {@code LinkProperties}. If there is a {@link RouteInfo}
+     * with the same destination, gateway and interface with different properties
      * (e.g., different MTU), it will be updated. If the {@link RouteInfo} had an
      * interface name set and that differs from the interface set for this
      * {@code LinkProperties} an {@link IllegalArgumentException} will be thrown.