[OVN] Do not check L3 agents state with ML2/OVN

With [1], the ML2/OVN L3 plugin will have the "ha" API extension
enabled. The OVN L3 plugin does not have L3 agents; this check
should be skipped.

[1]https://review.opendev.org/c/openstack/neutron/+/910889

Related-Bug: #2020823

Fixes-Bug: PRODX-42818

Change-Id: I09c12ba36b007d4f6fdd3723974ecfe9e4466b72
1 file changed