CtsNdkBinderTestCases: allow adding nullable

This doesn't change the wire protocol and doesn't affect code
generation. So, from a wire protocol, it's safe.

Bug: 146215188
Test: CtsNdkBinderTestCases
Change-Id: Ie08fc02dffd72a25b98d1c3ff818085f472ae728
(cherry picked from commit dd6f5886201c64cd25da410e745aba752546006a)
Merged-In: Ie08fc02dffd72a25b98d1c3ff818085f472ae728
10 files changed