si-adapter: handle autoconnect property

When the autoconnect property is not available or false, we must
simply configure the stream in its default channel map and leave it
unconnected.

Fixes pw-cat -p --target=0 ..
2 jobs for autoconnect in 1 minute and 9 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container
passed container_fedora #10516710

00:00:23

 
  Build
passed build_on_fedora #10516711

00:00:45