Ah, eu acho que eu mesmo entendi.
# Internet
allow-hotplug enx0050b6130ce2
iface enx0050b6130ce2 inet manual
pre-up ifup br0
down ifdown br0
# Bridge für LXC
iface br0 inet dhcp
bridge_ports enx0050b6130ce2
bridge_fd 0
bridge_maxwait 0