[systemd] Default to device 6 for snapclient

systemd/.config/systemd/user/snapclient.service

@@ -4,7 +4,7 @@ After=network.target
 
 [Service]
 EnvironmentFile="/etc/snapclient.env"
-ExecStart=/usr/bin/snapclient -h snapcast.service $EXTRA_ARGS
+ExecStart=/usr/bin/snapclient -h snapcast.service -s 6 $EXTRA_ARGS
 ExecStop=kill $(pidof snapclient)
 Restart=on-failure