staging: vt6656: move tx_body_size/payload_len to skb->len

both variables can be removed and replaced with skb->len.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/12e96cb5-a2a5-de3c-ebe7-ca5a4e2b5594@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>