Verify the size of data received based on tsize option

[dacitsme]

The tsize option can be used to verify the size of the received file after the transfer is complete. If the tsize does not match the number of octets received then the error packet can be sent as a response to the last data packet.

This is a second verification apart from ACK that the data received is complete.

I can contribute the changes if you think it is appropriate to include this.