Add EVPN monitoring with tenant-aware queries and ADD-PATH support

[jbemmel]

This PR adds support for monitoring BGP L2VPN EVPN routes through BGP and BMP, including ADD-PATH sessions.

What’s included

• Dedicated EVPN RIB — stores EVPN routes separately from global unicast, with identity based on route type, wire-format RD, route-specific keys, and ingress, including ADD-PATH identity.
• EVPN route decoding — decodes Type 2 MAC/IP and Type 5 IP prefix advertisements, partially decodes Types 1, 3, and 4, and preserves unknown RD-bearing route types as opaque records. Raw NLRI is retained for inspection.
• Route-target filtering — selects routes by advertised route target, allowing tenant-related state to be inspected across multiple RDs.
• Symmetric IRB visibility — exposes fields useful for correlating MAC-VRF and IP-VRF advertisements, including MAC/IP addresses, Ethernet tags, ESIs, gateways, both Type 2 label fields, router MAC communities, and next hops.
• Lifecycle handling — integrates EVPN into withdrawals, peer-down handling, and ingress cleanup, including address-family-scoped withdrawals. Route identity excludes applicable forwarding fields, so label changes do not prevent withdrawal matching.
• REST API and CLI — adds GET /api/v1/ribs/l2vpnevpn/routes and netom-cli show evpn, with filters for RD, route target, route type, VNI, prefix, ingress, and retained withdrawn routes.
• BMP output — includes EVPN in live rebuilt updates and initial RIB dumps, preserving next hops, communities, and ADD-PATH IDs.

Label fields are exposed as raw 24-bit values; the VNI filter matches these values for VXLAN monitoring. Withdrawn records are available when withdrawn-attribute retention is enabled.

Why this matters

EVPN monitoring provides visibility into advertised overlay state across tenants and forwarding domains. Route-target filtering supports inspection across multiple RDs, while separating route identity from forwarding attributes enables consistent tracking of route updates and withdrawals.

This provides a foundation for analyzing EVPN fabrics, correlating MAC-VRF and IP-VRF advertisements, and deriving resource inventories from observed control-plane data. It reports advertised state without inferring VRF membership, assigning L2/L3 VNI roles, or simulating import policy and forwarding resolution.