ath9k: Reconfigure tx power on regulatory update

Whenever the regulatory got updated by country IE for the world
roaming cards, need to reconfigure the tx power immediately to
increase the power level.

Reviewed-by: Sam Leffler <sleffler@google.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Acked-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>