NSR for BGP-Flowspec family inet and inet6

This feature adds nonstop active routing (NSR) support for BGP FlowSpec family inet and family inet6. NSR uses the same infrastructure as graceful Routing Engine switchover (GRES) to preserve interface and kernel information, while also preserving routing protocol state by running the routing protocol process (rpd) on the backup Routing Engine. This allows IPv4 and IPv6 BGP FlowSpec routing information and protocol state to be maintained across a Routing Engine switchover without relying on neighboring routers to support graceful restart extensions. BGP FlowSpec distributes traffic-filtering rules through BGP, enabling policy actions to be applied to matching IPv4 or IPv6 traffic. NSR helps preserve this FlowSpec state during a Routing Engine switchover.