iwlwifi: use mac80211_tx_control_flags

This patch makes use of the new mac80211_tx_control_flags and tx_rate to
pass Tx data, regular and 11n, from the HW tx response into the rate scaling.

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>