wl1271: Configure rates for templates

Configure meaningful rates to be used with the templates. For control frames,
use the determined basic rates (currently the lowest rate for the band) and
for data-frames (null-funcs) let the firmware use the current rate policy to
determine the rate.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>