Change HIDL fmq tests to use int32_t for payload

This is in preperation for more AIDL fmq testing. The types need to be
the same and AIDL does not support unit16_t.

Test: atest fmq_test fmq_unit_tests
Bug: 142326204
Change-Id: Ice9c28c3d0df064ea43c31950b3438d2e0d19063
3 files changed