bgpd: replay routes for every BGP instance to zebra

[0n41rd4]

When zebra restarts while bgpd keeps running, routes owned by a tenant
VRF BGP instance stay in the BGP RIB but are missing from zebra and the
kernel FIB. The reconnect replay from #22362 covers the default instance.

Closes: #23271

[greptile-apps]

Greptile Summary

The PR restores tenant-VRF BGP routes after zebra reconnects by registering every BGP instance already known to zebra and replaying each instance’s selected FIB-eligible routes.

• Preserves default-instance graceful-restart capability handling.
• Adds a tenant-VRF topotest covering route restoration after zebra-only restart.
• Consolidates the test topology’s daemon configuration into integrated FRR configuration files.
• Saves and restores the host udp_l3mdev_accept setting modified by the test.

Confidence Score: 5/5

The PR appears safe to merge, with no outstanding correctness or repository-rule violations identified.

The reconnect path now iterates only over BGP instances already known to zebra, re-registers each one, and replays its FIB-eligible tables; the tenant-VRF test directly checks route restoration after zebra restarts. The previous host-sysctl finding was manually resolved and the current teardown restores the saved value.

Important Files Changed

Filename	Overview
bgpd/bgp_zebra.c	Expands zebra reconnect registration and route replay from the default BGP instance to every zebra-known BGP instance.
tests/topotests/zebra_reconnect_route_replay/test_zebra_reconnect_route_replay_vrf.py	Adds tenant-VRF replay coverage and restores the host sysctl during teardown.
tests/topotests/zebra_reconnect_route_replay/vr1/frr.conf	Defines the originating router’s integrated tenant-VRF configuration for OSPF, RIP, IS-IS, and BGP.
tests/topotests/zebra_reconnect_route_replay/vr2/frr.conf	Defines the receiving router’s integrated tenant-VRF configuration used to verify route replay.

Sequence Diagram

sequenceDiagram
    participant B as bgpd
    participant Z as zebra
    participant K as Kernel FIB

    Z->>B: Reconnect
    B->>Z: Register BFD client
    loop Every BGP instance known to zebra
        B->>Z: Register BGP instance
        loop Every FIB-eligible AFI/SAFI
            B->>Z: Replay selected routes
            Z->>K: Reinstall routes
        end
    end

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_{Reviews (2): Last reviewed commit: "tests: add VRF variant of zebra reconnec..." | Re-trigger Greptile}

[ton31337-hostinger]

Please convert topotest using frr.conf (instead of per-daemon files)..

[0n41rd4]

@greptile review

[0n41rd4]

ci:rerun

[0n41rd4]

Hi @ton31337 , i pushed the changes

[0n41rd4]

ci:rerun

[0n41rd4]

changed router-ids to documentation range