wl12xx: declare support for IEEE80211_HW_REPORTS_TX_ACK_STATUS

The wl12xx fw supports ack status reporting for tx frames, so
add the IEEE80211_HW_REPORTS_TX_ACK_STATUS flag to our supported
features.

Since we do the rate control in the fw, we'll probably want
to adjust the STA_LOST_PKT_THRESHOLD heuristics in the future, to
account for retransmissions as well.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>