wlcore: use basic rates for non-data packets

After the latest mac80211 changes, the sta has
the ap's sta pointer even before association.

This cause the auth and assoc frames to be sent
with the standard ap's rates, rather than the
basic rates.

Change the tx rate policy logic to use the regular
ap rates only for data packets (so control and mgmt
packets will be sent with basic rates)

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>