Fix thinko with how bitfields were added to mp_obj_fun_native_t.

Structure is back to expected 16 bytes.

py/obj.h

@@ -54,7 +54,7 @@ typedef struct _mp_obj_base_t mp_obj_base_t;
 
 #define MP_DECLARE_CONST_FUN_OBJ(obj_name) extern const mp_obj_fun_native_t obj_name
 
-#define MP_DEFINE_CONST_FUN_OBJ_VOID_PTR(obj_name, is_kw, n_args_min, n_args_max, fun_name) const mp_obj_fun_native_t obj_name = {{&fun_native_type}, is_kw, n_args_min, n_args_max, (void *)fun_name}
+#define MP_DEFINE_CONST_FUN_OBJ_VOID_PTR(obj_name, is_kw, n_args_min, n_args_max, fun_name) const mp_obj_fun_native_t obj_name = {{&fun_native_type}, {is_kw, n_args_min}, n_args_max, (void *)fun_name}
 #define MP_DEFINE_CONST_FUN_OBJ_0(obj_name, fun_name) MP_DEFINE_CONST_FUN_OBJ_VOID_PTR(obj_name, false, 0, 0, (mp_fun_0_t)fun_name)
 #define MP_DEFINE_CONST_FUN_OBJ_1(obj_name, fun_name) MP_DEFINE_CONST_FUN_OBJ_VOID_PTR(obj_name, false, 1, 1, (mp_fun_1_t)fun_name)
 #define MP_DEFINE_CONST_FUN_OBJ_2(obj_name, fun_name) MP_DEFINE_CONST_FUN_OBJ_VOID_PTR(obj_name, false, 2, 2, (mp_fun_2_t)fun_name)
@@ -354,8 +354,10 @@ mp_obj_t mp_obj_new_bytearray_by_ref(uint n, void *items);
 // functions
 typedef struct _mp_obj_fun_native_t { // need this so we can define const objects (to go in ROM)
     mp_obj_base_t base;
+    struct {
         bool is_kw : 1;
-    machine_uint_t n_args_min : (sizeof(machine_uint_t) - 1); // inclusive
+        machine_uint_t n_args_min : (8 * sizeof(machine_uint_t) - 1); // inclusive
+    };
     machine_uint_t n_args_max; // inclusive
     void *fun;
     // TODO add mp_map_t *globals