usbhid-ups: fix cyberpower issues resolved when debug logging is enabled

[com6056]

Fixes #3116 which is caused by a slight difference in behavior when NUT_DEBUG_LEVEL is set, see full explanation here: #3116 (comment)

When running with these changes, I no longer see the disconnects after a couple minutes with my CP1500PFCLCDa 🎉

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Additional work may be needed after posting this PR

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[AppVeyorBot]

✅ Build nut 2.8.4.3925-master completed (commit 32d68f0c26 by @com6056)

[jimklimov]

Interesting catch, just shy of two decades old. I see this PR also adds explorehidall flag to usbhid-ups - can you please add documentation to the man page (and a mention in NEWS.adoc) about it please?

Also, I think its default value should be just zero, a VAR_FLAG mention sets it to 1 but otherwise there is no way to set it to 0. So it is not un-settable on CPS devices where this could cause a problem, and it remains -1 (so true in if clauses) by default on others. Maybe better redefine it as a VAR_VALUE and parse as zero/nonzero.

Also not sure if fflush(stdout) is needed there (at least nowadays, upsdebugx outputs are on stderr), and if either flush should be fenced by if (should_output_debug) {...} or remain unconditional.

[jimklimov]

Regarding the disconnections you saw, are there any logs from around then - why did the driver decide to reconnect? Maybe the "correct" solution is to ensure the cps-hid.c subdriver polls certain data points that is currently lacks in the mapping table?

[com6056]

Sorry for the delay, this actually didn't solve the issue. I've done some further digging and think I've found another potential solution though 🤞 Will push up the new changes when I can!
UPDATE: See #3259

[jimklimov]

Aha... and here I was, bringing this PR into better shape :)

For the next one, please post from a dedicated feature branch (not an existing one like master) to simplify resync later on.