Repository: syncthing/syncthing (language: go)

Issue:
Unresolvable stun.syncthing.net domain is still used by default
### What happened?

As seen in [stun.syncthing.net doesn’t resolve anymore](https://forum.syncthing.net/t/stun-syncthing-net-doesnt-resolve-anymore/24075/2?u=marbens) on the forums, stun.syncthing.net has been shut down, so I don't think it should still be referred to by default.

### Syncthing version

v1.29.3

### Platform & operating system

Arch Linux (64-bit AMD)

### Browser version

_No response_

### Relevant log output

```shell
2025-03-30 05:51:32 Enabled debug data for "stun"
2025-03-30 05:51:47 Starting stun for Stun@udp://[::]:22000
2025-03-30 05:51:47 Running stun for Stun@udp://[::]:22000 via stun.syncthing.net:3478
2025-03-30 05:51:47 Stun@udp://[::]:22000 stun addr resolution on stun.syncthing.net:3478: lookup stun.syncthing.net: no such host
2025-03-30 05:56:47 Starting stun for Stun@udp://[::]:22000
2025-03-30 05:56:47 Running stun for Stun@udp://[::]:22000 via stun.syncthing.net:3478
2025-03-30 05:56:47 Stun@udp://[::]:22000 stun addr resolution on stun.syncthing.net:3478: lookup stun.syncthing.net: no such host
2025-03-30 06:01:47 Starting stun for Stun@udp://[::]:22000
2025-03-30 06:01:47 Running stun for Stun@udp://[::]:22000 via stun.syncthing.net:3478
2025-03-30 06:01:47 Stun@udp://[::]:22000 stun addr resolution on stun.syncthing.net:3478: lookup stun.syncthing.net: no such host
2025-03-30 06:06:47 Starting stun for Stun@udp://[::]:22000
2025-03-30 06:06:47 Running stun for Stun@udp://[::]:22000 via stun.syncthing.net:3478
2025-03-30 06:06:47 Stun@udp://[::]:22000 stun addr resolution on stun.syncthing.net:3478: lookup stun.syncthing.net: no such host
```


Discussion / hints:

Fix patch:
diff --git a/lib/config/config.go b/lib/config/config.go
index 772694859b2..935f66d3427 100644
--- a/lib/config/config.go
+++ b/lib/config/config.go
@@ -71,7 +71,8 @@ var (
 
 	// DefaultPrimaryStunServers are servers provided by us (to avoid causing the public servers burden)
 	DefaultPrimaryStunServers = []string{
-		"stun.syncthing.net:3478",
+		// Discontinued because of misuse. See https://forum.syncthing.net/t/stun-server-misuse/23319
+		//"stun.syncthing.net:3478",
 	}
 	DefaultSecondaryStunServers = []string{
 		"stun.callwithus.com:3478",


Test patch: