mac80211_hwsim: Fix rate control by correctly reporting transmission counts

Drivers need to report the number of transmission attempts for each rate
as well as to terminate the rate array with -1.  The in-kernel datapath
of hwsim simulates a perfect medium, therefore the driver only needs to
report that the first transmission attempt was sucessfully completed at
the most favorable rate.

Rate control is working again for this driver.  Tested mesh mode with
minstrel.

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>