Deauth is sent to AP when the device is acting as station at
shutdown time. Similarly we should stop AP operation also.
mwifiex_deauthenticate() takes care closing the connection
based on provided interface type.

Add a new function to simplify the code.
Reported-by: NAvery Pennarun <apenwarr@gmail.com>
Signed-off-by: NAmitkumar Karwar <akarwar@marvell.com>
Signed-off-by: NBing Zhao <bzhao@marvell.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>