staging: vt6656: rxtx.c Parse struct vnt_tx_datahead_g

Parse struct vnt_tx_datahead_g from s_uFillDataHead and
move to struct vnt_rts_g/struct vnt_cts structure.

This removes pvTxDataHd pointer assignment.

The duration_id(uDuration) field is now returned in s_vGenerateTxParameter.

The return of s_uFillDataHead temporary or'ed to retain functionality of
other functions and is removed at the end of this patch series.

Since pvTxDataHd is now null a small vendor hack to vDMA0_tx_80211/csMgmt_xmit
to do with Disassociation-packet is also changed correct head position.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>