Call UUI deactivation callbacks when changing function via tty

[kanflo]

The following will cause "litter pixels" not visible when changing using the physical controls. Most likely the deactivation callbacks are not called.

% dpsctl -d /dev/cu.usbmodemC4D0B9DA3 -f funcgen
Changed function.
% dpsctl -d /dev/cu.usbmodemC4D0B9DA3 -f cv
Changed function.

[Xenoamor]

I can't find this in the code at a first glance. The call tree seems to be:

handle_set_function()
opendps_enable_function_idx()
uui_set_screen()

uui_set_screen should be calling the last screens deactivation function