When we are operating in passthrough, let the Start command pass through
to the follower in all cases. Only do the negotiate/buffers when not in
passthrough.
This fixes a case where the buffers are cleared on the alsa node and it
Pauses but then never resumes in a Start because the node is already
started. The real problem is probably somewhere else (in PipeWire) but
for now this will improve things in passthrough.
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