Notify port available status changes, and update protocol version

The recommended way of setting available status is to call
pa_device_port_set_available, which will send a subscription event
to the relevant card. It will also fire a hook.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>

src/pulsecore/core.h

@@ -113,6 +113,7 @@ typedef enum pa_core_hook {
     PA_CORE_HOOK_CARD_PUT,
     PA_CORE_HOOK_CARD_UNLINK,
     PA_CORE_HOOK_CARD_PROFILE_CHANGED,
+    PA_CORE_HOOK_PORT_AVAILABLE_CHANGED,
     PA_CORE_HOOK_MAX
 } pa_core_hook_t;