Statistics should be collected according to the actual rate a
frame/aggregation was transmitted and not according to the initial rate
from the last LQ command (these rates are different if the frames were
retransmitted at a lower rate from the rate scale table).

This is needed to remove throughput degradation.
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>