staging: vt6656: vnt_update_ifs set max_min based on short slot time.

Short slot time is controlled by mac80211 so there is no need to find
odfm rates.

Merge PK_TYPE_11B and PK_TYPE_11GA & PK_TYPE_11GB into one else and
switch on short slot time.

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