staging: vt6656: mac80211 conversion: enable power saving

Convert vnt_enable_power_saving and vnt_disable_power_saving

Remove mgmt->wCurrAID and use priv->current_aid

We nolonger send the PSbSendNullPacket from vnt_enable_power_saving

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