Exposing connect, disconnect and scan for now.
In case the iface is an instance of a WiFi offload device, the way it
manages scanning, connecting and disconnecting will be specific to that
device (not the mgmt interface obviously). In such case the device will
have to export relevantly a dedicated bunch of function to serve the
mgmt interface in a generic way.
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>