SR Enable Segment ID as FirstHop

The segment routing architecture enables ingress nodes in a core network to steer traffic through explicit paths through the network. The segment routing-traffic engineering (SR-TE) next hop is a list or lists of segment identifiers (SIDs). These segment lists represent paths in the network that incoming traffic should take. The incoming traffic may be labeled or IP traffic and the forwarding operation at the ingress node may be a label swap or a destination-based lookup to steer the traffic onto these SR-TE paths in the forwarding path. When SR-TE was initially implemented on Juniper devices, for a non-colored SR-TE LSP to be usable, the first hop of the segment list had to be an IP address of an outgoing interface. This feature introduces support for segment lists where the first hop of the non-colored static LSPs can be a SID label, instead of an IP address. With the first-hop label support, MPLS fast reroute (FRR) and weighted equal-cost multipath are enabled for resolving the static non-colored SR-TE LSPs.