bluetooth: Fix crash on disconnection

bluetooth: Fix crash on disconnection

When a Bluetooth headset is connected only to HFP profile (not connected
to A2DP) and host streams to it, a crash occurs if host disconnects.

When HFP disconnects, audio thread will fail on POLLHUP then generate
a message to set PA profile to Off before ending.
If this message is managed before PA unload bluetooth device module,
all works fine.
But, if this message is managed during module unload, this finish by
re-entrance in release code (stop_thread) and a crash.

This fix prevents to process profile change when module is unloading.