CHROMIUM: mesh: add mesh path debug log

Add plink broken debug log.
Add more mesh path log for debugging purpose.
Ported from CL:323338

BUG=b:133418819
TEST=manually test on mistral, logs show up in dmesg
Signed-off-by: Roy Luo <royluo@google.com>
Change-Id: I02caf210a984d733fafd6b9a4e29ccab4c7b5573
Reviewed-on: https://chromium-review.googlesource.com/1642720


Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Julan Hsu <julanhsu@google.com>