Fade transition is ok with computer but not in stand-alone

[support]

Box and Ssa interfaces have the following restriction in stand-alone mode: [fade time (in tens of seconds)] x [level variation] must less than 65536. This means for instance:
- from dmx level 0 to dmx level 63, fade time must be less than 100s
- from dmx level 64 to dmx level 127, fade time must be less than 100s
- from dmx level 128 to dmx level 255, fade time must be less than 50s
- from dmx level 0 to dmx level 255, fade time must be less than 25s

This restriction does not exist with other interfaces having stand-alone ability.