core: move generic connection complete function to a generic location

Out of NMDevice specific places to the utils code, so it can be used
more easily from everywhere.  There's nothing device-specific about
it anyway.

src/NetworkManagerUtils.h

@@ -78,4 +78,10 @@ gboolean nm_utils_get_proc_sys_net_value (const char *path,
                                           const char *iface,
                                           guint32 *out_value);
 
+void nm_utils_complete_generic (NMConnection *connection,
+                                const char *ctype,
+                                const GSList *existing,
+                                const char *format,
+                                const char *preferred);
+
 #endif /* NETWORK_MANAGER_UTILS_H */