device-port, switch-on-port-available: fix automatic profile changing when current...

device-port, switch-on-port-available: fix automatic profile changing when current profile is off

module-switch-on-port-available didn't do anything when a port changes
its status if the card didn't have any sinks or sources. This was to
avoid bad things during card initialization, but the if condition also
prevented any profile switches away from the "off" profile, because the
card has no sinks or sources when the "off" profile is active.

pa_card nowadays has the "linked" flag that
module-switch-on-port-available could have checked instead, but since it
doesn't make sense to emit port status change events before the card has
been initialized, I added the check in pa_device_port_set_available()
instead.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=101794