Validity of SR Policy Candidate Path

An SR Policy comprises one or more candidate paths of which at a given time one and only one may be active (i.e., installed in forwarding plane and usable for steering of traffic). Each candidate path, in turn, may have one or more segment lists of which one or more may be active. When multiple segment lists are active, traffic is load balanced over them. Currently, a candidate path is valid as long as at least one of its segment lists is active. However, this default validity criterion does not meet the requirements of some scenarios. This document defines the new candidate path validity criterion.