After testing, we found that TX_STA_FIFO_MCS is the last MCS value
tried. If the transmission failed, 8 frames have been transmitted. If the
transmission succeed, we can easily compute the number of retry.  This patch fix
the way status is reported to mac80211 rate control. It has 2 bugs :

1. mcs can contain the short preamble flag and it will lead to wrong
computations.

2. minstrel nearly always say that 54 Mbits is the best rate, even if we are
very far from the AP
Signed-off-by: NBenoit Papillault <benoit.papillault@free.fr>
Signed-off-by: NAlban Browaeys <prahal@yahoo.com>
Acked-by: NIvo van Doorn <ivdoorn@gmail.com>
Signed-off-by: NGertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>