security: fix: use default initialization instead of nanopb init_zero

Nanopb init_zero doesn't cover all fields on oneof entries. On 5.4 COS,
the unknown fields are replaced with 0xAA leading to a crash.

BUG=b/168558508
TEST=Integration tests.
SOURCE=KTD

Signed-off-by: Thomas Garnier <thgarnie@chromium.org>
Change-Id: Id24ca76587bce89e7cfde5fd4628b6d675a7adc6
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/6080
Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Reviewed-by: John Davis <kyuzo@google.com>
Reviewed-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
(cherry picked from commit 81aec0f01b2da82430d9816a25a6643c48e2642a)
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/6120
Reviewed-by: Roy Yang <royyang@google.com>
3 files changed