op-mode add `MAC` , `VRF `and `MTU` for `show interfaces summary`
```
vyos@r4# run show interfaces summary
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address MAC VRF MTU S/L Description
----------- ----------------- ----------------- ------- ----- ----- -------------
dum0 203.0.113.1/32 96:44:ad:c5:a1:a5 default 1500 u/u
eth0 192.168.122.14/24 52:54:00:f1:fd:77 default 1500 u/u WAN
eth1 192.0.2.1/24 52:54:00:04:33:2b foo 1500 u/u LAN-eth1
eth2 - 52:54:00:40:2e:af default 1504 u/u LAN-eth2
eth3 - 52:54:00:09:a4:b4 default 1500 A/D
eth4 - 52:54:00:2c:51:09 default 1500 A/D
eth5 - 52:54:00:f3:1d:e8 default 1500 A/D
lo 127.0.0.1/8 00:00:00:00:00:00 default 65536 u/u
::1/128
vtun10 10.10.0.1/24 n/a default 1500 u/u
[edit]
vyos@r4#
```