[OVN] OVN agent extensions correctly consume agent API

Now the ``OVNAgentExtension`` class do not clear the agent API during
the extension initialization.

This patch also passes the agent object to the OVN agent extensions
as agent API. Any method required will be implemented directly on the
OVN agent class.

Closes-Bug: #2046939
Change-Id: Ia635ca1ff97c3db43a34d3dec6a7f9df154dfe28
(cherry picked from commit 86efc8b)

Author: ralonsoh

neutron/agent/ovn/agent/ovn_neutron_agent.py

@@ -59,7 +59,7 @@ def __init__(self, conf):
         self.ovn_bridge = None
         self.ext_manager_api = ext_mgr.OVNAgentExtensionAPI()
         self.ext_manager = ext_mgr.OVNAgentExtensionManager(self._conf)
-        self.ext_manager.initialize(None, 'ovn', self.ext_manager_api)
+        self.ext_manager.initialize(None, 'ovn', self)
 
     @property
     def ovs_idl(self):

neutron/agent/ovn/extensions/extension_manager.py

@@ -50,7 +50,7 @@ def __init__(self):
 
     def initialize(self, *args):
         """Initialize agent extension."""
-        self.agent_api = None
+        pass
 
     def consume_api(self, agent_api):
         """Configure the Agent API.