utils: add nm_utils_modprobe()

https://bugzilla.gnome.org/show_bug.cgi?id=740651

src/NetworkManagerUtils.h

@@ -51,6 +51,8 @@ nm_utils_ip6_route_metric_normalize (guint32 metric)
 
 int nm_spawn_process (const char *args);
 
+int nm_utils_modprobe (GError **error, const char *arg1, ...) G_GNUC_NULL_TERMINATED;
+
 /* check if @flags has exactly one flag (@check) set. You should call this
  * only with @check being a compile time constant and a power of two. */
 #define NM_FLAGS_HAS(flags, check)  \