Document that Route::route_params will be required soon

This field was always set since 0.0.117, so in the next version we're going to
make it officially required.

Author: valentinewallace

lightning/src/routing/router.rs

@@ -683,7 +683,8 @@ pub struct Route {
 	///
 	/// This is used by `ChannelManager` to track information which may be required for retries.
 	///
-	/// Will be `None` for objects serialized with LDK versions prior to 0.0.117.
+	/// Will be `None` for objects serialized with LDK versions prior to 0.0.117. This field will
+	/// soon move to being required and must always be set.
 	pub route_params: Option<RouteParameters>,
 }