fix: linux baudRate and latency errors

[reconbot]

• linuxGetLowLatencyMode would incorrectly get an error
• linuxSetLowLatencyMode would incorrectly get an error
• linuxGetSystemBaudRate would incorrectly get an error
• linuxSetCustomBaudRate would incorrectly get an error

Thanks to @GazHank for highlighting work was needed in this area

[reconbot]

@GazHank I don't have a linux machine handy, would you be able to test this branch?

[GazHank]

With the parentheses change per above, I'm getting successful results:

• setting DTR true etc seems to work
• no errors when setting low latency with admin rights
• suitable error messages when access rights don't permit setting low latency

I've tested on:

• Ubuntu 20.04.2 LTS
• Node.js 14.16.0,
• Chromium 89.0.4389.128,
• Electron 12.0.9

I should call out that I'm not really able to test that low latency mode works, only that it doesn't seem to break stuff anymore :-)

Additionally I've tried sending some dodgy values (0 and very large numbers) to the update baudrate, and so far I've not managed to trigger any error codes (I double checked and this is the case with or without the change to linuxSetCustomBaudRate, so I don't think we have broken anything.

[reconbot]

I think dodgy baudrates are a serial driver concern less a linux kernel concern and they seem to have chosen to silently ignore them in general. Hense we have this bolted on readBaudrate method, which maybe setBaudrate should be calling to check it's work.

[GazHank]

@reconbot let me know if there are any extra tests you'd like me to run. I'm normally on Win10, but can fire up Linux for some testing if I can help

[reconbot]

Thank you =)

[reconbot]

#1676 already exists 🤷