policy-node: forward filter stream's format to filter device

Currently, when using filter nodes such as echo-cancel or filer-chain, the ports format of the virtual stream node might not always match the format of its associated virtual device node. This can happen if the virtual stream node is linked with a real device node configured with many channels, such as surround profile. In that case, the channel configuration is not forwarded to the virtual device node, making the application not being aware of a surround setup.

This change listens for port format changes in the virtual stream nodes, and reconfigures the virtual device node ports every time the virtual stream node's port format changes.

This behavior is experimental and optional, so it is disabled by default.