…pv6 only topologies sonic-net#21377 (sonic-net#888)

Manual cherry-pick of PR[
sonic-net#21377](sonic-net#21377)

Adjust test_bgpmon.py to handle running over ipv6 only topologies

[Vxlan] : adding show vnet/vxlan cmds (sonic-net#880)
[show][bgp] Use only 'show ip bgp' as the base and use bgp_frr_v4 file
for FRR routing stack (sonic-net#884)
[fast reboot] set a fast-reboot DB flag (sonic-net#887)
[show] Add 'ip/ipv6 bgp network' commands (sonic-net#888)

```
*   d849917 (HEAD -> user/r12f/merge-202412, origin/user/r12f/merge-202412, internal-202412) r12f 260209:0619 - Merge remote-tracking branch 'azure/202412' into internal-202412
|\
| * c4c429c (azure/202412) mssonicbld 260209:0115 - [action] [PR:21843] Fix test_bgp_suppress_fib.py flakiness on scale topos (sonic-net#1011)
| * 46503f1 Mark Xiao 260205:1058 - [202412] Fix test_acl.py [ipv6-ingress-uplink->downlink-*] cases for v6 topo (sonic-net#942)
| * b6c58d4 mssonicbld 260130:1215 - [action] [PR:21772] Fix test_bgp_suppress_fib.py for v6 topos (sonic-net#985)
| * e762451 mssonicbld 260130:1016 - [action] [PR:21762] Fix test_disk_exhaustion.py for v6 topos (sonic-net#983)
| * 02cadbb mssonicbld 260130:1016 - [action] [PR:21771] Fix test_bgp_bounce.py for v6 topos (sonic-net#984)
| * 7eab3e7 Priyansh 260129:1437 - [202412] Fix/nonlinear dataplane downtime (sonic-net#982)
| * de89a46 mssonicbld 260130:0616 - [action] [PR:21143] configlet/test_add_rack.py Add comparison ignore for extra entries added by generic patcher (sonic-net#977)
| * c731442 mssonicbld 260130:0616 - [action] [PR:21647] Remove test_route_flow_counter.py xfail for v6 topos (sonic-net#979)
| * 0ff3ecc mssonicbld 260130:0116 - [action] [PR:21717] [BGP][test_bgp_session.py::test_bgp_session_interface_down] - Increase BGP Session State Timeout Window when restarting SWSS Container (sonic-net#978)
| * e0a408c Mark Xiao 260129:0914 - [202412] Fix fib/test_fib.py test_vxlan_hash [ipv6-*] (sonic-net#971)
| * 51b0525 mssonicbld 260124:0615 - [action] [PR:21523] Feature/route programming data (sonic-net#974)
| * 2bb2a53 mssonicbld 260124:0615 - [action] [PR:21939] Fix/nonlinear high nexthop dataplane downtime (sonic-net#975)
| * 1fe73bc Mark Xiao 260123:1323 - [202412] Fix setup_interfaces fixture and related bgp tests for v6 topo (sonic-net#941)
| * fda4ac2 Chuan Wu 260124:0520 - Enhance PTF function at scale testbed (sonic-net#913)
| * e8edcae gshemesh2 260123:2317 - Manual cherry-pick PR: Adjust test_bgpmon.py to handle running over ipv6 only topologies sonic-net#21377 (sonic-net#888)
| * 24b3dc7 gshemesh2 260123:2313 - Manual cherry-pick of PR: Adjusting test_stress_arp is it can handle cases of ipv6-only topologies . sonic-net#20932 (sonic-net#923)
```

----
#### AI description  (iteration 1)
#### PR Classification
This pull request is a feature enhancement that adds and refines IPv6 compatibility across multiple BGP, ACL, and related test modules.

#### PR Summary
The changes extend the testing framework and helper utilities to support IPv6-only and dual-stack environments by conditionally switching commands, packet generation, and route verifications.
- `tests/bgp/test_bgpmon.py` and `tests/bgp/test_bgp_update_timer.py`: Updated function signatures and logic to construct, verify, and clean up IPv6 routes and packets (e.g., using /64 and /128 prefixes).
- `tests/bgp/test_bgp_suppress_fib.py` and `tests/bgp/test_bgp_peer_shutdown.py`: Modified commands and packet filters to support IPv6 addressing and proper neighbor session handling.
- `tests/common/...` files and generators: Integr...