Description of problem:

The following tests fail:

networking_ovn.tests.unit.ml2.test_mech_driver.TestOVNMechansimDriverSegment.test_clear_segment_host_mapping

networking_ovn.tests.unit.ml2.test_mech_driver.TestOVNMechansimDriverSegment.test_update_segment_host_mapping

The failure is: 

{"NeutronError": {"type": "InvalidInput", "message": "Invalid input for operation: Requested MTU is too big, maximum is 1450.", "detail": ""}}


Version-Release number of selected component (if applicable):  latest OSP 12


How reproducible: 100%


Steps to Reproduce:
1. Clone networking-ovn and checkout rhos-12.0-patches branch
2. Run unit tests

Actual results:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/neutron/tests/base.py", line 118, in func
    return f(self, *args, **kwargs)
  File "networking_ovn/tests/unit/ml2/test_mech_driver.py", line 1325, in test_clear_segment_host_mapping
    _, host = self._test_segment_host_mapping()
  File "networking_ovn/tests/unit/ml2/test_mech_driver.py", line 1307, in _test_segment_host_mapping
    network_type='geneve')['segment']
  File "/usr/lib/python2.7/site-packages/neutron/tests/unit/extensions/test_segment.py", line 124, in _test_create_segment
    segment = self.segment(**keys)
  File "/usr/lib/python2.7/site-packages/neutron/tests/unit/extensions/test_segment.py", line 120, in segment
    self.fmt, tenant_id=self._tenant_id, **kwargs)
  File "/usr/lib/python2.7/site-packages/neutron/tests/unit/extensions/test_segment.py", line 114, in _make_segment
    code=res.status_int, explanation=str(res))
webob.exc.HTTPClientError: 400 Bad Request
Content-Length: 142
Content-Type: application/json; charset=utf8

{"NeutronError": {"type": "InvalidInput", "message": "Invalid input for operation: Requested MTU is too big, maximum is 1450.", "detail": ""}}


Expected results: Tests passed successfully