cmd/stdiscosrv: Deduplicate addresses (fixes #8482) (#9080)

cmd/stdiscosrv/apisrv.go

@@ -29,6 +29,7 @@ import (
 	"time"
 
 	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/syncthing/syncthing/lib/stringutil"
 )
 
 // announcement is the format received from and sent to clients
@@ -440,6 +441,9 @@ func fixupAddresses(remote *net.TCPAddr, addresses []string) []string {
 		fixed = append(fixed, uri.String())
 	}
 
+	// Remove duplicate addresses
+	fixed = stringutil.UniqueTrimmedStrings(fixed)
+
 	return fixed
 }