Stablize the test by adding pause after the route change

Signed-off-by: Shu0T1an ChenG <shuche@microsoft.com>

…v6 topo (sonic-net#942)

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### Description of PR
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Summary:
t0-isolated-v6-*:
Downstream neighbors are servers connected to VLAN interface. Use
DOWNSTREAM_DST_IP_VLAN as dest ips. IPv6 cases have been skipped for t0
since beginning, only fix it for v6 topos now.

t1-isolated-v6-*:
V6 topo files set ipv6_address_pattern:
2064:100:0::%02X%02X:%02X%02X:0/120.
announce_routes.py uses the pattern to generate routes for PTF and pass
them to VMs. If it is not set, default pattern
20%02X:%02X%02X:0:%02X::/64 is used.
acl tests use hardcoded dest ip 20c0:a800::1 that is not covered by v6
topo pattern, so packets are forwarded with the default route to
upstream VM.
Fix it by changing dest ip for v6 topos, also add acl rules for these
dest ips.

With extra ACL rules for v6 topos, also increase timeout for
check_rule_counters.

Manual cherry pick of sonic-net#21760

### Type of change

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- Fill x for your type of change.
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- [x] Bug fix
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- [ ] Bug fix
- [ ] Testbed and Framework(new/improvement)
- [ ] New Test case
    - [ ] Skipped for non-supported platforms
- [x] Test case improvement


### Back port request
- [x] 202412
- [x] 202505

### Approach
#### What is the motivation for this PR?
test_acl.py [ipv6-ingress-uplink->downlink-*] cases failed on v6 topo

#### How did you do it?
Correct DOWNSTREAM_DST_IP for t0/t1-isolated-v6-*. topos, and add
corresponding acl rules

#### How did you verify/test it?
Test passed on t0/t1-isolated-v6-*. topos

#### Any platform specific information?

#### Supported testbed topology if it's a new test case?

### Documentation
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(If it's a new feature, new test case)
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Link to the wiki page?
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---------

Signed-off-by: markxiao <markxiao@arista.com>

 [201911][thermal control] Backport changes from master branch (sonic-net#929)
     [201911][config] Support abbreviation (sonic-net#933)
       Add 'hw-management-generate-dump.sh' to 'show techsupport'
       command (sonic-net#934)
       [fwutil]: Update fwutil to v2.0.0.0. (sonic-net#942)
       Fixes bug for PFCWD feature parameters (sonic-net#838)
     Fixed fast-reboot for BFN platform (sonic-net#871)
     [config] Add 'interface transceiver' subgroup with 'lpmode' and
     'reset' subcommands (sonic-net#904)
      [warm-reboot]: added pre-check for ISSU file (sonic-net#915)
       [config] Don't attempt to restart disabled services (sonic-net#944)

```
*   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)
```

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#### 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...