floss: btmanagerd: Replace i32 with VirtualHciIndex / RealHciIndex

Some code are still using i32 to indicate HCI devices. Apply the type
to them to avoid passing the index in different meaning.

Bug: 306322786
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Toggle BT through ChromeOS UI, verified state machine
      and callbacks work fine
Change-Id: Ic0b73ca45b4b3d13a752f60a27c338eb81621c36