mwifiex: separate uAP WPA/WPA2 parsing from other BSS parameters

To enhance readability, create a separate function for parsing
WPA/WPA2 related parameters from cfg80211_ap_settings.
There is no functional change in this patch.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>