rea/app:dock:: fix hide problem.

1. if dock is started with hide mode setted to always hide, then changing
hide mode to keep showing, the workarea is not changed to dock height.
2. dock can be hidden after setting menu is shown.

reason:
1. the hide_mode is not updated on C.
2. not handled that.

Change-Id: I042e871f1aa86713230602f674dd4eaf6a46ee10