Add a simple passive TFO server and client test binary. This will be
used to test the SO_INCOMING_NAPI_ID of passive TFO accepted sockets.
Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://patch.msgid.link/20250617212102.175711-3-dw@davidwei.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
