mac80211: init HT TX data before rate control

In case of connection, the station data is initialised from
the beacon/probe response first and then updated from the
association response. If the latter is different we update
the rate control algorithm and driver. Instead of doing it
this way, set the station data properly with data from the
association response before initializing rate control.

Also simplify the code by passing the station pointer.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>