Monkey patch original current_thread _active

Monkey patch the original current_thread to use the up-to-date _active
global variable. This solution is based on that documented at:
eventlet/eventlet#592

Change-Id: I5ea4bb27361df3c489deedb51d7ca8ea64bb923b
Closes-Bug: #1863021

networking_bagpipe/agent/bagpipe_ml2/agent_extension.py

@@ -17,6 +17,12 @@
 
 import eventlet
 eventlet.monkey_patch()
+# Monkey patch the original current_thread to use the up-to-date _active
+# global variable. See https://bugs.launchpad.net/bugs/1863021 and
+# https://github.com/eventlet/eventlet/issues/592
+import __original_module_threading as orig_threading  # pylint: disable=E0401
+import threading  # noqa
+orig_threading.current_thread.__globals__['_active'] = threading._active
 
 from oslo_concurrency import lockutils
 from oslo_config import cfg