add IPv6 routing tests converted from SAI PTF

[illia-smulskyi]

Summary

Convert 9 test cases from SAI PTF to SAI Challenger:

• test_ipv6_host_route
• test_ipv6_lpm_route
• test_ipv6_prefix_lengths
• test_ipv6_ecmp_host
• test_ipv6_ecmp_lpm
• test_ipv6_lag_route
• test_ipv6_neighbor_mac_update
• test_ipv6_neighbor_fdb_ageout
• test_ipv6_ecmp_group_member_update

Source reference

PTF test cases were ported from:
usecases/sai-ptf/SAI/test/saithrift/tests/sail3.py

Run all IPv6 routing tests

./exec.sh -t saivs pytest --testbed=saivs_standalone -v -k "test_ipv6_route"

Test results (saivs standalone)

======================= test session starts =========================
platform linux -- Python 3.11.2, pytest-9.0.3, pluggy-1.6.0 -- /usr/bin/python3
cachedir: .pytest_cache
metadata: {'Python': '3.11.2', 'Platform': 'Linux-6.17.0-22-generic-x86_64-with-glibc2.36', 'Packages': {'pytest': '9.0.3', 'pluggy': '1.6.0'}, 'Plugins': {'metadata': '3.1.1', 'html': '4.2.0', 'dependency': '0.6.1'}}
rootdir: /sai-challenger/tests
configfile: pytest.ini
plugins: metadata-3.1.1, html-4.2.0, dependency-0.6.1
collected 1514 items / 1505 deselected / 9 selected

test_ipv6_route.py::test_ipv6_host_route PASSED [ 11%]
test_ipv6_route.py::test_ipv6_lpm_route PASSED [ 22%]
test_ipv6_route.py::test_ipv6_prefix_lengths PASSED [ 33%]
test_ipv6_route.py::test_ipv6_ecmp_host PASSED [ 44%]
test_ipv6_route.py::test_ipv6_ecmp_lpm PASSED [ 55%]
test_ipv6_route.py::test_ipv6_lag_route PASSED [ 66%]
test_ipv6_route.py::test_ipv6_neighbor_mac_update PASSED [ 77%]
test_ipv6_route.py::test_ipv6_neighbor_fdb_ageout PASSED [ 88%]
test_ipv6_route.py::test_ipv6_ecmp_group_member_update PASSED [100%]

===================== 9 passed, 1505 deselected in 22.33s ==============