rndis_wlan: disable stall workaround

Stall workaround doesn't work with bcm4320a devices like with bcm4320b.
This workaround actually causes more stalls/device freeze on bcm4320a.
Therefore disable stall workaround by default.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>