MdeModulePke/Mtftp4Dxe: Support windowsize in read request operation.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=886

This patch is to support the TFTP windowsize option described in RFC 7440.
The feature allows the client and server to negotiate a window size of
consecutive blocks to send as an alternative for replacing the single-block
lockstep schema.

Currently, the windowsize for write request operation is not supported since
there is no real use cases.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Shao Ming <ming.shao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>

MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Support.h

@@ -173,19 +173,6 @@ Mtftp4SendError (
   IN UINT8                  *ErrInfo
   );
 
-/**
-  Retransmit the last packet for the instance.
-
-  @param  Instance              The Mtftp instance
-
-  @retval EFI_SUCCESS           The last packet is retransmitted.
-  @retval Others                Failed to retransmit.
-
-**/
-EFI_STATUS
-Mtftp4Retransmit (
-  IN MTFTP4_PROTOCOL        *Instance
-  );
 
 /**
   The timer ticking function in TPL_NOTIFY level for the Mtftp service instance.