[BUG] EVPN control-plane-only nodes do not work with VXLAN/IPv6

[ipspace]

The EVPN AF logic relies on VXLAN VTEP AF to figure out which neighbor to activate. That attribute is not set/copied on EVPN control-plane-only nodes, and so the EVPN AF is not activated for IPv6 neighbors. Having EVPN AF on IPv6 transport session requires vxlan module on the node

To Reproduce

See evpn/41-vxlan-ipv6-bridging.yml

[jbemmel]

Perhaps extend evpn.transport with a vxlan6 value?

And then reinterpret control-plane-only nodes as the ones not having the vxlan/mpls/etc. module enabled