BluetoothHAL: Reset the chip on open(), close once

Sending a reset and discarding extra packets
helps ensure that tests are hermetic for devices
that do not power off the chip with rfkill.

Add a mutex to make sure that close only gets
called once.

Bug: 266221125
Test: atest VtsHalBluetoothTargetTest
Change-Id: Ifb259a675202aa5399a8c7570ba8c4df2083e10e