[Snappi] IPv6 Route withdraw is giving exception

[selldinesh]

Version information
snappi 0.9.1
snappi-convergence 0.4.1
snappi-ixnetwork 0.9.1

Describe the bug
Using snappi_convergence while trying to do route withdraw for v4 and v6 routes, i was getting the below exception
`
18:47:52 bgp_performance_pr.get_route_install_tim L0447 INFO | Withdraw All Routes before starting traffic
18:48:09 snappi_api.info L1132 INFO | Setting route state 0.000s
18:48:09 init.pytest_runtest_call L0040 ERROR | Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/snappi_ixnetwork/snappi_convergence_api.py", line 133, in set_state
event_names = self._api.ngpf.set_route_state(route)
File "/usr/local/lib/python3.8/dist-packages/snappi_ixnetwork/device/ngpf.py", line 280, in set_route_state
ixn_obj_idx_list[route_info].extend(list(range(
KeyError: <snappi_ixnetwork.objectdb.IxNetInfo object at 0x7fd36d5c0190>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/_pytest/python.py", line 1788, in runtest
self.ihook.pytest_pyfunc_call(pyfuncitem=self)
File "/usr/local/lib/python3.8/dist-packages/pluggy/_hooks.py", line 513, in call
return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
File "/usr/local/lib/python3.8/dist-packages/pluggy/_manager.py", line 120, in _hookexec
return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
File "/usr/local/lib/python3.8/dist-packages/pluggy/_callers.py", line 139, in _multicall
raise exception.with_traceback(exception.traceback)
File "/usr/local/lib/python3.8/dist-packages/pluggy/_callers.py", line 103, in _multicall
res = hook_impl.function(*args)
File "/usr/local/lib/python3.8/dist-packages/_pytest/python.py", line 194, in pytest_pyfunc_call
result = testfunction(**testargs)
File "/var/AzDevOps/sonic-mgmt/tests/snappi_tests/multidut/bgp/test_bgp_performance_route_install_multiple_sessions.py", line 81, in test_bgp_route_install
run_bgp_route_install_test(api=cvg_api,
File "/var/AzDevOps/sonic-mgmt/tests/snappi_tests/multidut/bgp/files/bgp_performance_pr.py", line 55, in run_bgp_route_install_test
get_route_install_time(api,
File "/var/AzDevOps/sonic-mgmt/tests/snappi_tests/multidut/bgp/files/bgp_performance_pr.py", line 449, in get_route_install_time
cs = api.convergence_state()
File "/usr/local/lib/python3.8/dist-packages/snappi_ixnetwork/snappi_convergence_api.py", line 143, in set_state
raise SnappiIxnException(err)
snappi_ixnetwork.exceptions.SnappiIxnException: <exception str() failed>

FAILED [100%]
--------------------------------------------------------------------------- live log teardown ----------------------------------------------------------------------------
`

To Reproduce

    route_names = ['IPv6_Routes_0', 'IPv6_Routes_1']
    cs = api.convergence_state()
    cs.route.names = route_names
    cs.route.state = cs.route.WITHDRAW
    api.set_state(cs)

Expected behavior
It should withdraw both v4 and v6 routes

Additional context
for v4 routes i don't see any issue,

    route_names = ['IPv4_Routes_0', 'IPv4_Routes_1']
    cs = api.convergence_state()
    cs.route.names = route_names
    cs.route.state = cs.route.WITHDRAW
    api.set_state(cs)

this code works fine