all: Use MP_REGISTER_EXTENSIBLE_MODULE for overrideable built-ins.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

extmod/modbluetooth.c

@@ -1004,7 +1004,11 @@ const mp_obj_module_t mp_module_bluetooth = {
     .globals = (mp_obj_dict_t *)&mp_module_bluetooth_globals,
 };
 
-MP_REGISTER_MODULE(MP_QSTR_bluetooth, mp_module_bluetooth);
+// This module should not be extensible (as it is not a CPython standard
+// library nor is it necessary to override from the filesystem), however it
+// has previously been known as `ubluetooth`, so by making it extensible the
+// `ubluetooth` alias will continue to work.
+MP_REGISTER_EXTENSIBLE_MODULE(MP_QSTR_bluetooth, mp_module_bluetooth);
 
 // Helpers