linux-info: sync with upstream for pkg_setup fixes

getfilevar has a fix to avoid creating $S too soon with bad
permissions.  Otherwise just comment/style tweaks.

BUG=chromium:1105501
TEST=CQ passes

Change-Id: Ie1780b20d77f94cc026b11420906b4caaefcf63e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/2311412
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>