Merge "[Thread] add error code ERROR_UNKNOWN for forward compatibility" into main am: 649571ddf7

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2910724

Change-Id: I8e8647f0a7379c6bfd8c299fa6e599ef14ede494
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>