Summary:
When I add "efl_event_callback_add(btn, EFL_GFX_ENTITY_EVENT_VISIBILITY_CHANGED, _cb, NULL)",
_cb is not called. Because of callback_mask is not set correctly.
Test Plan: unit test
Reviewers: zmike, cedric
Subscribers: #reviewers, #committers
Tags: #efl
Differential Revision: https://phab.enlightenment.org/D8528