VPP unexpected default MTU `9000` for bonding interface
```
vyos@r14# run show conf com | match vpp
set interfaces vpp bonding vppbond2 member interface 'eth1'
set interfaces vpp bonding vppbond2 mode 'active-backup'
set vpp settings interface eth1
set vpp settings poll-sleep-usec '2222'
[edit]
vyos@r14# run show interfaces vpp
Kernel Dataplane Type IP Address MAC MTU State
-------- ------------- ------ ------------ ----------------- ----- -------
BondEthernet2 bond 52:54:00:f4:d5:cd 9000 up
eth1 dpdk 52:54:00:f4:d5:cd 1500 up
local0 local 00:00:00:00:00:00 0 down
eth1 tap4096 virtio 02:fe:36:06:73:38 1500 up
vppbond2 tap4097 virtio 02:fe:c6:83:c4:96 9000 up
[edit]
vyos@r14#
```