Uncomment jack_set_port_rename_callback() since it seems to work

[xkr47]

Comment suggested "doesn't compile for testing since it is a weak export" but I was able to compile and run tests just fine. I have Linux / Devuan with jack2 (not pipewire).

A few tests were failing, but commenting or uncommenting the code did not affect the outcome.

I changed this since I maintain a program to automatically update connections based on which (jack) clients and ports are present and I noticed Ardour seems to rename ports.. and I would prefer to not having to request a full list of ports and connections on every event..

Thanks for your great lib!