floss: Align the meaning of the index in the pid file name

btadapterd composes the pid file name with virtual index, while
btmanagerd treats it as real index.
This may cause problems when the real index changes, such as USB
disconnection, firmware crashes, and waking from hibernation.

Bug: 302559622
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: echo 1 > /sys/class/bluetooth/hci?/device/coredump to trigger
      HCI index change
Change-Id: I8709b1062ad0f1bef18da72fb01daec1042b6020