staging: vt6656: Move calling point of vnt_fill_txkey.

Change vnt_fill_txkey to return true if mic_hdr is needed and
change calling point at where it is to be placed.

tx_buffer is already in tx_context.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/f08a6f07-a77e-0b8e-cb05-505a1f995683@gmail.com


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