set dhcp_agent_manager for ovs plugin

related to bug 1131446, makes makes this setting no longer the default,
as doing so broke DHCP for other plugins.

Change-Id: I01ff9e00ba8d416179b485000e69cf3b3908b7bf
diff --git a/lib/quantum_plugins/openvswitch b/lib/quantum_plugins/openvswitch
index 181e7e7..726c6c3 100644
--- a/lib/quantum_plugins/openvswitch
+++ b/lib/quantum_plugins/openvswitch
@@ -31,7 +31,7 @@
 }
 
 function quantum_plugin_configure_dhcp_agent() {
-    :
+    iniset $Q_DHCP_CONF_FILE DEFAULT dhcp_agent_manager quantum.agent.dhcp_agent.DhcpAgentWithStateReport
 }
 
 function quantum_plugin_configure_l3_agent() {