Revert "[eventlet-removal] Remove the usage of eventlet in the DHCP agent"

This reverts commit 7c32d43c4b.

Reason for revert: the DHCP agent is still using "oslo.service". The
only backend implemented so far is "eventlet" (see c#2 in LP#2101840).
This revert is temporary until we have a "oslo.service" release
using kernel libraries.

This patch is reverted along with [1], that is proposed on top of this
patch.

[1]https://review.opendev.org/c/openstack/neutron/+/942393

Partial-Bug: #2101840
Change-Id: Ifd4f10a65935d9779ae4b5329258aef6bd5f871b

neutron/tests/fullstack/agents/dhcp_agent.py

@@ -21,7 +21,7 @@ from oslo_config import cfg
 from oslo_utils import uuidutils
 
 from neutron.agent.linux import dhcp as linux_dhcp
-from neutron.cmd.agents import dhcp as dhcp_agent
+from neutron.cmd.eventlet.agents import dhcp as dhcp_agent
 from neutron.common import config
 
 

setup.cfg

@@ -34,7 +34,7 @@ wsgi_scripts =
     neutron-api = neutron.cmd.server:main_api_uwsgi
 console_scripts =
     neutron-db-manage = neutron.db.migration.cli:main
-    neutron-dhcp-agent = neutron.cmd.agents.dhcp:main
+    neutron-dhcp-agent = neutron.cmd.eventlet.agents.dhcp:main
     neutron-keepalived-state-change = neutron.cmd.keepalived_state_change:main
     neutron-ipset-cleanup = neutron.cmd.ipset_cleanup:main
     neutron-l3-agent = neutron.cmd.eventlet.agents.l3:main