replace them with NL80211_IFTYPE_ macros

Also remove redundant functions mwifiex_drv_get_mode()
and mwifiex_bss_ioctl_mode().
Signed-off-by: NBing Zhao <bzhao@marvell.com>
Signed-off-by: NAmitkumar Karwar <akarwar@marvell.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>