binder_ndk: fix read/write interface

To meet the legacy CPP behavior, reading and writing null interface
values is okay even when @nullable is not specified in AIDL.

Bug: 151817759
Test: atest CtsNdkBinderTestCases
Change-Id: I6f33e5ce1071f52681988fd6c1b6b8f30923c8b2
1 file changed