Some network monitoring systems require that the index interface not change after a reboot. Linux allows you to create interfaces with a manually specified interface index. Example:

ip link add bond0 index 101 type bond
ip link add link bond0 name bond0.1 index 102 type vlan id 1

I suggest adding an interface configuration option. Example:

set interfaces bonding bond0 index 101
set interfaces bonding bond0 vif 1 index 102