ZTP: In-band ZTP in EVPN multihoming deployments

In-band ZTP now supports EVPN multihoming deployments that use Layer 2 Integrated Routing and Bridging (IRB) interfaces. In EVPN multihoming topologies, downstream devices can establish redundant connections to multiple upstream devices during Day0 provisioning. Upstream devices participate in an EVPN-VXLAN fabric provide Layer 3 onboarding connectivity through DHCP relay services.