Change the default l3_agent_manager to L3NATAgent

This is a l3-agent version of 349aa3e.

The combination of the plugin without agent extension support
and L3NATAgentWithStateReport results in an error:
"AttributeError: No such RPC function 'report_state'".

This patch changes l3_agent_manager to be L3NATAgent instead of
L3NATAgentWithStateReport since all plugins do not support
L3NATAgentWithStateReport and having this as the default breaks
all current deployments that upgrade source without changing
their config files.

Fixes bug 1139726

Change-Id: Ibb5c04c89bfad741ec43a372cbf97445f7b3d76c

etc/l3_agent.ini

@@ -2,6 +2,9 @@
 # Show debugging output in log (sets DEBUG log level output)
 # debug = True
 
+# The Quantum L3 Agent manager
+# l3_agent_manager = quantum.agent.l3_agent.L3NATAgent
+
 # L3 requires that an interface driver be set.  Choose the one that best
 # matches your plugin.
 

quantum/agent/l3_agent.py

@@ -144,7 +144,7 @@ class L3NATAgent(manager.Manager):
                    help=_("UUID of external network for routers implemented "
                           "by the agents.")),
         cfg.StrOpt('l3_agent_manager',
-                   default='quantum.agent.l3_agent.L3NATAgentWithStateReport',
+                   default='quantum.agent.l3_agent.L3NATAgent',
                    help=_("The Quantum L3 Agent manager.")),
     ]