libnm: rename NetworkManager.h and NetworkManagerVPN.h

"NetworkManager.h"'s name (and non-standard capitalization) suggest
that it's some sort of high-level super-important header, but it's
really just low-level D-Bus stuff. Rename it to "nm-dbus-interface.h"
and likewise "NetworkManagerVPN.h" to "nm-vpn-dbus-interface.h"

src/platform/wifi/wifi-utils.h

@@ -25,7 +25,7 @@
 #include <net/ethernet.h>
 #include <glib.h>
 
-#include "NetworkManager.h"
+#include "nm-dbus-interface.h"
 
 typedef struct WifiData WifiData;