mwifiex: disconnect the device before entering suspend state

By default, device is disconnected before entering suspend state.
User can keep the connection alive by using module parameter
"disconect_on_suspend=0".

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>