Function del_routes_to_subnet 

pub fn del_routes_to_subnet<I: IpLayerIpExt, BT: IpRoutingBindingsTypes, CC: IpRouteTablesContext<I, BT>>(
    core_ctx: &mut CC,
    del_subnet: Subnet<I::Addr>,
) -> Result<(), NotFoundError>

Delete all routes to a subnet, returning Err if no route was found to be deleted.

Note, del_routes_to_subnet will remove all routes to a subnet, including routes that consider subnet on-link for some device and routes that require packets destined to a node within subnet to be routed through some next-hop node.