Make the read ahead buffer unselectable

Here is the email loop talk about why it is better to remove the option:
https://groups.google.com/forum/#!topic/nuttx/AaNkS7oU6R0

Change-Id: Ib66c037752149ad4b2787ef447f966c77aa12aad
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

fs/procfs/fs_procfsiobinfo.c

@@ -136,13 +136,13 @@ static FAR const char *g_iob_user_names[] =
 #ifdef CONFIG_NET_BLUETOOTH
   "bluetooth_sock",
 #endif
-#ifdef CONFIG_NET_UDP_READAHEAD
+#if defined(CONFIG_NET_UDP) && !defined(NET_UDP_NO_STACK)
   "udp_readahead",
 #endif
 #ifdef CONFIG_NET_UDP_WRITE_BUFFERS
   "udp_writebuffer",
 #endif
-#ifdef CONFIG_NET_TCP_READAHEAD
+#if defined(CONFIG_NET_TCP) && !defined(NET_TCP_NO_STACK)
   "tcp_readahead",
 #endif
 #ifdef CONFIG_NET_TCP_WRITE_BUFFERS