floss: Refactor create_adapter_proxy

create_adapter_proxy is better to be a method instead of associated
function because it operates on itself. Additionally, passing i32 is
simpler to be done by value instead of by reference.

Bug: 199213563
Tag: #floss
Test: Manual

Change-Id: I5f34aaf93f69e9be02223ee3ccfa5c778417f9fd