Demote log statement to trace

It is known to overflow logs and cause high cpu usage. We don't know why it appeared so late though, as it worked for years without issues.

Author: Brutus5000

ice-adapter/src/main/java/com/faforever/iceadapter/ice/PeerConnectivityCheckerModule.java

@@ -69,7 +69,7 @@ synchronized void stop() {
      */
     void echoReceived(byte[] data, int offset, int length) {
         if (length != 9) {
-            log.warn("Received echo of wrong length, length: {}", length);
+            log.trace("Received echo of wrong length, length: {}", length);
         }
 
         int rtt = (int) (System.currentTimeMillis() - Longs.fromByteArray(Arrays.copyOfRange(data, offset + 1, length)));