ath5k: do not stop queues for full calibration

Some calibration types interfere with tx activity, but the queue stop does
not prevent that. In fact, some calibration types need tx activity to properly
function, so stopping the queues for them is counterproductive.
In some tests this patch has been shown to improve stability, especially in
AP or ad-hoc mode.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>