creation of multiple streams that are not destroyed

[dorindabassey]

The regular PCM command lifecycle for playing a stream is SET_PARAMS -> PREPARE -> START -> STOP ->RELEASE -> SET_PARAMS-> PREPARE -> ..........
but there are some exceptional cases that do not follow the regular PCM command lifecycle, like in the case of using sox tool to play audio from the guest, to test this:
start the vhost-user-sound daemon on the host with pipewire backend option enabled and enable rust debug on the daemon
Install sox tool on the guest and run play /usr/share/sounds/alsa/Front_Left.wav from the guest.
The order of PCM commands using this tool is SET_PARAMS -> PREPARE -> SET_PARAMS -> PREPARE -> SET_PARAMS -> PREPARE -> START -> STOP ->RELEASE -> .........
This order of PCM commands is also valid sequence of commands however this scenario lead to multiple creation of pipewire streams that are not destroyed. We need to ensure that in a case like this, when the prepare fn() in the pipewire backend is called multiple times without the release fn(), there should be only one pipewire stream.

[stefano-garzarella]

Moved upstream rust-vmm#490