nl80211: Fix re-enabling of 802.11b rates

nl80211: Fix re-enabling of 802.11b rates

nl80211_disable_11b_rates() function was supposed to use the 'disabled'
parameter to figure out whether to disable or re-enable 802.11b rates.
In addition, the driver deinit path was now ending up re-disabling the
enabled rates at the end of the deinit operations when the interface
type was forced back to station. Both of these issues are now fixed
and the 2.4 GHz band TX rate index is cleared properly when
wpa_supplicant is stopped.

Signed-hostap: Jouni Malinen <j@w1.fi>