ShellPkg: Add argument to set block size for tftp command.

TFTP block size has a big impact on the transmit performance, this patch is to
add new argument [-s <block size>] for shell "tftp" command to configure the
block size for file download.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

ShellPkg/Library/UefiShellTftpCommandLib/UefiShellTftpCommandLib.uni

@@ -1,7 +1,7 @@
 // /**
 //
 // (C) Copyright 2015 Hewlett Packard Enterprise Development LP<BR>
-// Copyright (c) 2010 - 2011, Intel Corporation. All rights reserved. <BR>
+// Copyright (c) 2010 - 2016, Intel Corporation. All rights reserved. <BR>
 // This program and the accompanying materials
 // are licensed and made available under the terms and conditions of the BSD License
 // which accompanies this distribution. The full text of the license may be found at
@@ -50,7 +50,7 @@
 ".SH SYNOPSIS\r\n"
 " \r\n"
 "TFTP [-i interface] [-l <port>] [-r <port>] [-c <retry count>] [-t <timeout>]\r\n"
-"     host remotefilepath [localfilepath]\r\n"
+"     [-s <block size>] host remotefilepath [localfilepath]\r\n"
 ".SH OPTIONS\r\n"
 " \r\n"
 "  -i interface     - Specifies an adapter name, i.e., eth0.\r\n"
@@ -61,6 +61,8 @@
 "                     wait for a response. The default value is 6.\r\n"
 "  -t <timeout>     - The number of seconds to wait for a response after\r\n"
 "                     sending a request packet. Default value is 4s.\r\n"
+"  -s <block size>  - Specifies the TFTP blksize option as defined in RFC 2348.\r\n"
+"                     Valid range is between 8 and 65464, default value is 512.\r\n"
 "  host             - Specify TFTP Server IPv4 address.\r\n"
 "  remotefilepath   - TFTP server file path to download the file.\r\n"
 "  localfilepath    - Local destination file path.\r\n"