In patch [1] it was by mistake set to "legacy" but it should be
"legacy_l2".
This patch fixes that mistake.
Closes-bug: #1917448
[1] https://review.opendev.org/c/openstack/neutron/+/763204
Conflicts:
neutron/tests/functional/agent/common/test_ovs_lib.py
Change-Id: Idb743bbfd5454b8d245c4dd4b8c3d7021e90d238
(cherry picked from commit 1dbe389392)