WNM: Differentiate between WNM for station and for AP in build

WNM: Differentiate between WNM for station and for AP in build

Previously, CONFIG_WNM enabled build that supports WNM for both
station mode and AP mode. However, in most wpa_supplicant cases only
station mode WNM is required and there is no need for AP mode WNM.

Add support to differentiate between station mode WNM and AP mode
WNM in wpa_supplicant builds by adding CONFIG_WNM_AP that should be
used when AP mode WNM support is required in addition to station mode
WNM. This allows binary size to be reduced for builds that require
only the station side WNM functionality.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>