staging: vt6656: vnt_tx_packet use skb_clone to preserve sk_buff.

The sk_buff needs to preserved for copying to various parts
of context and passing back to mac80211

clone sk_buff in context so to continue to writing to orginal
sk_buff data area to send in vnt_tx_context.

dev_kfree_skb the context on error or dev_kfree_skb the
orignal when done. The error handling continues as before.

Only one place in function needs to change from
ieee80211_get_hdrlen_from_skb to ieee80211_hdrlen(hdr) which
is already to pointing to correct position.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/b87e8cc1-f584-989d-830b-609d712f08c7@gmail.com


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