NetworkManager is Linux specific and to be able to build geoclue, other
platforms (BSD) build with WiFi source disabled. Now that we don't have
a separate geoip source, geoclue will be completely useless on those
platforms.

This patch replaces '--disable-wifi-source' configure option with
'--disable-network-manager'. i-e now you disable usage of NetworkManger
explicitly rather than wifi source, which is now always built and
enabled.