(cherry-pick) daemon: Only write DDC brightness after reading and comparing first
Cherry-pick MR for !456 (merged).
Anecdotal evidence suggests that repeated writes to the NVRAM of some monitors will reduce its lifespan. This has recently been confirmed by vdu_controls developer Michael Hamilton: https://github.com/digitaltrails/vdu_controls/blob/master/README.md#does-adjusting-a-vdu-affect-its-lifespan-or-health
One way to reduce NVRAM writes is to avoid writing brightness if the current hardware brightness is already the same as the requested value. This commit implements such a check in DDCutilDisplay.
Some monitors may already have a similar check implemented in firmware, however, others may not. Checking first is the safe thing to do, and mirrors what recent vdu_controls releases have been doing.
(cherry picked from commit 2a267fcf)
Co-authored-by: Jakob Petsovits jpetso@petsovits.com