staging: vt6656: vnt_rxtx_rsvtime_le16 to use ieee80211_generic_frame_duration.

ieee80211_generic_frame_duration is the mac80211 equivalent to
vnt_get_rsvtime use this to get our frame time.

There is a change where there is rrv_time_a and rrv_time_b
the frame duration is always the same so both are equal.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/acff7fcc-0add-652b-7d07-22001b641257@gmail.com


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