usb: code cleanup and add a few comments

11 jobs for usbv6_udev in 16 minutes and 1 second (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #280554
build

00:13:57

 
  Test
passed #280556
asan

00:02:03

passed #280555
test

00:01:55

 
  Manual
manual #280561
allowed to fail manual
armv8
manual #280557
allowed to fail manual
flatpak
manual #280560
allowed to fail manual
msan
manual #280562
allowed to fail manual
ppc64le
manual #280558
allowed to fail manual
tsan
manual #280559
allowed to fail manual
ubsan
 
  Review
manual #280563
allowed to fail manual
review
manual #280564
allowed to fail manual
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