Switched to pyroute2.config.asyncio.asyncio_config

To monkey patch socket module for pyroute2, we call eventlet_config.
In recent releases of the library, this becomes deprecated. Instead, we
should now use asyncio_config() to patch stdlib.

Using the old path now triggers a warning. Our docs tox target (and
gate job) considers all warnings as errors (this is because we pass -W
to sphinx). We also import from neutron.tests.functional to generate one
of our docs pages. Which all combined breaks our docs job.

This patch fixes the warning, and the job.

Change-Id: I7554327c9f09c85b52293240b23133eeadc90670
Closes-Bug: #1694614

neutron/common/eventlet_utils.py

@@ -22,5 +22,5 @@
 def monkey_patch():
     eventlet.monkey_patch()
     if os.name != 'nt':
-        p_c_e = importutils.import_module('pyroute2.config.eventlet')
-        p_c_e.eventlet_config()
+        p_c_e = importutils.import_module('pyroute2.config.asyncio')
+        p_c_e.asyncio_config()