The supported_rates field should contain all our supported
rates, even if the remote peer doesn't support them.

(rename CONF_TX_AP_ENABLED_RATES to CONF_TX_ENABLED_RATES,
as we now use it for both ap and sta)
Signed-off-by: Eliad Peller <eliad@wizery.com>
Reviewed-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>