Removed:
* stun.l.google.com:19302
* stun.bluesip.net:3478
* stun.dus.net:3478
* stun.sonetel.net:3478
* stun.voys.nl:3478

Added:
* stun.mixvoip.com:3478
* stun.nextcloud.com:3478
* stun.bethesda.net:3478
* stun.nextcloud.com:443

I also removed a bunch of servers from the tm settings because not all
of them support NAT behaviour discovery on the alternate port.