mac80211: Fix regression on queue stop during 2040 bss change

The commit "mac80211: stop tx before doing hw config and
rate update" stops the tx queue and call drv_flush so frequently
whenever a beacon got received with 11n htcap. This leads to
massive "Failed to stop TX DMA" logspam on embedded hw. So the
queue stop and flush should be called if and only if there is a
change in the channel type.

Reported-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>