ath9k: optimize rate control statistics

for the ease of debugging, we display only the rate control statistics
for currently operating mode and bandwidth

Cc: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Cc: "Balasubramanian, senthilkumar" <senthilb@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>