Some platforms really don't like DMA bursts of 256 bytes, and this
causes the firmware to crash when sending beacons.
Also, changing this based on the firmware version does not seem to make
much sense, so use 128 bytes for all versions.

Cc: stable@vger.kernel.org
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NKalle Valo <kvalo@qca.qualcomm.com>