Set l3_agent_manager for ovs/linuxbridge plugin

related to quantum bug 1139726, L3NATAgentWithStateReport makes
no longer the default, as doing so broke DHCP for other plugins.

Quantum linuxbridge has the agent extension support. This commit also
set dhcp/l3_agent_manager to *AgentWithStateReport in linuxbridge plugin.

Change-Id: I4095f4276499468d02265169cc26bbd8489679bc
diff --git a/lib/quantum_plugins/openvswitch b/lib/quantum_plugins/openvswitch
index 726c6c3..8df1246 100644
--- a/lib/quantum_plugins/openvswitch
+++ b/lib/quantum_plugins/openvswitch
@@ -36,6 +36,7 @@
 
 function quantum_plugin_configure_l3_agent() {
     _quantum_ovs_base_configure_l3_agent
+    iniset $Q_L3_CONF_FILE DEFAULT l3_agent_manager quantum.agent.l3_agent.L3NATAgentWithStateReport
 }
 
 function quantum_plugin_configure_plugin_agent() {