mwifiex: skip registering mgmt frame that has already registered

Before sending command to firmware, we need to check the frame type.
We skip registering the mgmt frame that has already been registered.

Signed-off-by: Stone Piao <piaoyun@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>