Add a separate data structure for MBSSID parameters

Add a separate data structure for MBSSID parameters

The MBSSID related parameters are present under struct
wpa_driver_ap_params, but this is not extensible for certain use cases
like updating the MBSSID and RNR elements post channel switch. Hence,
move this into a separate data structure named mbssid_data to hold all
MBSSID related parameters in a manner that can be used more easily
elsewhere.

Signed-off-by: Manish Dharanenthiran <manish.dharanenthiran@oss.qualcomm.com>