mwl8k: force AP mode to use non-AMPDU frames

AP firmware uses xmitcontrol to differentiate between AMPDU
and non-AMPDU frames. As the support for AMPDU is not yet
added, set xmitcontrol to non-AMPDU for all tx frames for AP
firmware. This field will be set to indicate ampdu/non-ampdu
frames when tx AMPDU support is added.

Signed-off-by: Pradeep Nemavat <pnemavat@marvell.com>
Signed-off-by: Brian Cavagnolo <brian@cozybit.com>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>