Fix bug where GameService#onDisconnected isn't called

As it is, since the disconnected call happens in
unbind, the call is immediately dropped due to the
unbinding instead of going through. This change is a
quick fix that makes it so that unbind always
happens after disconnect.

Bug: 223981361
Test: atest CtsGameServiceTestCases
Change-Id: Icd331e64dd2be80829b8baead521906bb7d41bae