floss: Use devpath to determine virtual hci index

While we depended directly on hci index for tracking adapters, we found
races with the kernel that could sometimes affect the ordering. This
refactor separates the hci index into |VirtualHciIndex| and
|RealHciIndex| so that we can keep the same virtual index even when the
real hci index changes.

Bug: 244457509
Tag: #floss
Test: Manual testing on Realtek Zork
Change-Id: Ia601e917328728350bacf5cf3600790fb707e1c1