test-trace_buffer: increase thread stack to 8K

Prevents warnings on x86_32/linux.

repos/os/src/test/trace_buffer/main.cc

@@ -168,7 +168,7 @@ struct Test_thread : Thread
 	}
 
 	Test_thread(Env &env, Trace::Buffer &buffer, unsigned delay)
-	: Thread(env, "producer", 1024 * sizeof(addr_t)),
+	: Thread(env, "producer", 8*1024),
 	  env(env),
 	  buffer(buffer),
 	  delay(delay)