Use 2 dhcp agents in TestLegacyL3Agent
Use 2 dhcp agents in TestLegacyL3Agent

This is a workaround for privsep hanging issue described in bug 1930401.
Proper fix is developed in
https://review.opendev.org/c/openstack/neutron/+/794994
- this fix will revert current change to reproduce and verify
privsep issue is fixed.

Related-Bug: #1930401
Change-Id: I143cd55612118f243c0e502fb77a611d1ee48761

openstack/neutron,mahak/neutron,openstack/neutron,mahak/neutron,mahak/neutron,openstack/neutron