VPN Services Over Colored SR-TE Tunnels: RIB-group fallback to LDP LSP

This feature introduces LDP label-switched path (LSP)-based next-hop resolution fallback for VPN services over colored segment routing-traffic engineering (SR-TE) LSPs. The fallback from colored SR-TE LSPs to LDP LSPs is a simple process, and it uses a RIB group to install routes in the inet{6}color.0 routing tables. A longest prefix match for a colored-IP protocol next hop ensures that if a colored SR-TE LSP route does not exist, an LDP route with a matching IP address should be returned.