Fix BTM callbacks so callee and caller types match

This CL fixes inconsistencies between the actual type of a callback
function, and the type assumed at the call site. This respects the
intended function signature.

For P, we plan to enable control-flow integrity (CFI) across multiple
platform components, including BT. This mismatch will break CFI and
cause runtime errors when enabled - so this is also a preemptive
measure to get BT compatible in preparation.

Bug: 30227045
Test: Builds and runs without errors when CFI is enabled.
Change-Id: I8970e6866d8b37a9adf5e040db993d30f1b5103a