Steps to reproduce:
configure interface and vrrp
```
set interfaces ethernet eth1 vif 92 address '192.168.112.14/31'
set high-availability vrrp group v92 interface 'eth1.92'
set high-availability vrrp group v92 no-preempt
set high-availability vrrp group v92 priority '110'
set high-availability vrrp group v92 virtual-address '172.18.92.1/24'
set high-availability vrrp group v92 vrid '4'
```
my router owns both ip's on eth1.92, because I am **not** using `rfc3768-compatibility`
```
olof@vyos:~$ show interfaces ethernet eth1 vif 92
eth1.92@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 00:50:56:bc:ff:21 brd ff:ff:ff:ff:ff:ff
inet 192.168.112.14/31 scope global eth1.92
valid_lft forever preferred_lft forever
inet 172.18.92.1/24 scope global eth1.92
valid_lft forever preferred_lft forever
```
then configure dhcp-relay
`set service dhcp-relay interface 'eth1.92'`
When tcpdumping the dhcp-relay packets, I can see that the vyos router is sending with the "wrong" `relay-agent-address`, it is using `192.168.112.14`.
Now, the problem, is that there is no subnet scope defined on the dhcp-server that uses 192.168.112.14/31.
If the dhcp-relay-agent-address would have been the vrrp-IP `172.18.92.1`, the server would understand which dhcp-scope to use.