thunderbolt: Make the DP tunnel activation callback mandatory

In the Linux kernel, the following vulnerability has been resolved: thunderbolt: Make the DP tunnel activation callback mandatory tb_tunnel_alloc_dp() takes an optional callback which is run from dprx_work once the DPRX capabilities read has completed. Without that callback tb_dp_dprx_start() reads the capabilities synchronously and never queues the work. It however always takes a tunnel reference which is only dropped by dprx_work itself or by tb_dp_dprx_stop() when cancel_delayed_work() actually canceled that work. That reference is thus leaked for every tunnel without a callback. The only tunnels without one are those from tb_tunnel_discover_dp(), which are activated again when restoring from hibernation. Pass the callback to tb_tunnel_discover_dp() as well and drop the synchronous path such that the DPRX capabilities are always read from dprx_work. Hibernation restore then also no longer blocks for up to 12 seconds while waiting for that read to complete. Also fix up the KUnit tests.