[Thread] make Thread flags fixed_read_only am: 8fb3f07dfe

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3243931

Change-Id: I0f2119e23fcaec880073a0f4128b4a421295454a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>