Support VLAN tunnel mapping of VLAN aware bridges
https://legacy.netdevconf.info/2.2/slides/prabhu-linuxbridge-tutorial.pdf
https://www.google.com.hk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwji79Pl6P3xAhUOxWEKHdxHCyQQFjABegQIBhAD&url=https%3A%2F%2Fblog.csdn.net%2Fsinat_20184565%2Farticle%2Fdetails%2F90487687&usg=AOvVaw0b92WLJKFxm8fHFQ5ERRq8
example:
```
set interfaces l2tpv3 l2tpeth0 tunnel-id 2000
set interfaces l2tpv3 l2tpeth0 peer-tunnel-id 2000
set interfaces l2tpv3 l2tpeth0 session-id 2000
set interfaces l2tpv3 l2tpeth0 peer-session-id 2000
set interfaces l2tpv3 l2tpeth0 source-address <local address>
set interfaces l2tpv3 l2tpeth0 remote <remote address>
commit
set interfaces bridge br1 enable-vlan
set interfaces bridge br1 vif 20
set interfaces bridge br1 member interface eth0 vlan-tunnel 2000 vlan 2000
commit
```