Improve the spa_ump_to_midi function so that it can consume multiple UMP
messages and produce multiple midi messages.
Some UMP messages (like program changes) need to be translated into up
to 3 midi messages. Do this byt adding a state to the function and by
making it consume the input bytes, just like the spa_ump_from_midi
function.
Adapt code to this new world. This is a little API break..
Always listen on the receive socket. Find the stream with the given
stream_name of the packet and create it if it doesn't exist.
Also take the sample-rate, channels and format from the packet
parameters instead of the config.
Fixes#4400
