staging: vt6656: Move vnt_tx_usb_header to vnt_tx_context

staging: vt6656: Move vnt_tx_usb_header to vnt_tx_context

Move the USB element out of vnt_tx_packet and vnt_beacon_xmit to
vnt_tx_context with sk_buff passed in parameters with the data now
between skb->data and skb->len.

The vnt_tx_usb header is moved from vnt_tx_buffer to usbpipe.h with the
size added to extra_tx_headroom the largest possible size.

The CONTEXT enums types are aligned with usb ones and CONTEXT_MGMT_PACKET
is removed and is never be used.

The skb_push in vnt_tx_packet is now only ever used with
vnt_get_hdr_size with variables tx_bytes and tx_header_size removed.

buf_len in vnt_usb_send_context is no longer used and replaced with
urb->actual_length in vnt_tx_context_complete.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/aa6257eb-1758-4e75-ab39-2a15ff6ffa7c@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>