device-port: fire port available changed hook after streams are moved

If port becomes unavailable then PA_CORE_HOOK_PORT_AVAILABLE_CHANGED callbacks may eventually destroy related source or sink object. When sink is destroyed moving it reads from freed memory as indicated in #1008 (closed).

Call this hook after stream is moved to prevent crash.

This change partially reverts !310 (merged) so Gnome behaviour should be validated. I do not run Gnome so did not verified that part.

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