Support VLAN tunnel mapping of VLAN aware bridges
https://legacy.netdevconf.info/2.2/slides/prabhu-linuxbridge-tutorial.pdf
https://blog.csdn.net/sinat_20184565/article/details/90487363
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
```