sync ml2 plugin api

Commit I3e91669a83e9e16039f4063bf54b511cec94cecc updated the ml2 driver
api. This patch syncs the change into lib.

Change-Id: I38d3a09d7d358ea9cb97d526c46a2a0806652c1e

neutron_lib/plugins/ml2/api.py

@@ -1037,6 +1037,16 @@ class ExtensionDriver(object):
         """
         pass
 
+    @property
+    def extension_aliases(self):
+        """List of extension aliases supported by the driver.
+
+        Return a list of aliases identifying the core API extensions
+        supported by the driver. By default this just returns the
+        extension_alias property for backwards compatibility.
+        """
+        return [self.extension_alias]
+
     def process_create_network(self, plugin_context, data, result):
         """Process extended attributes for create network.
 

releasenotes/notes/rehome-ml2-api-extaliases-4db48e113893c7a5.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - The ``ExtensionDriver`` class in ``neutron_lib.plugins.ml2.api`` now
+    contains the ``extension_aliases`` property to match neutron's
+    implementation.