mwifiex: remove unnecessary enum MWIFIEX_802_11_WEP_STATUS

Instead of defining an 'enum', we can simply use 'u8' flag for WEP
status. Rename 'wep_status' to 'wep_enabled' to match with
'wpa_enabled' and 'wpa2_enabled'.

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>