sound: Ignore loopbacks

These are used in pipewire/wireplumber for role based routing policies and are thus not useful to display to the user. Role based policies are not yet enabled by default in wireplumber.

Before

After

Adding separate volume sliders for the roles associated with the loopbacks will make sense at some point but as that is still settling in regarding wp support, roles, icons, etc. this might be a bit premature for 50 (I have a prototype in p-m-s which we could the move over). This just makes sure things continue to function as before should the user drop in a role based policy.

Signed-off-by: Guido Günther agx@sigxcpu.org