During firewall rewriting, a new constraint was added for [inbound-interface | outbound-interface] interface-name.
In the past, it was possible to introduce VRF name as a interface.
Now with this new constraint it is no longer possible.

Constraint should be remove or extend, in order to allow vrf name.

Constraint introduced in PR https://github.com/vyos/vyos-1x/pull/2142