Retry ebtables lock acquisition failures

It seems after the merge of
https://bugs.launchpad.net/ubuntu/+source/ebtables/+bug/1645324
that ebtables can fail to acquire a lock and bail with an error
255. This adds some retry logic to retry it up to 10 times to
work around this issue.

Closes-Bug: #1697833
Change-Id: Ic9dcf4b236a93e8811413c6ce2c4b82602544c6d
(cherry picked from commit 2e7b787f0e)

neutron/plugins/ml2/drivers/linuxbridge/agent/arp_protect.py

@@ -16,6 +16,7 @@
 import netaddr
 from oslo_concurrency import lockutils
 from oslo_log import log as logging
+import tenacity
 
 from neutron._i18n import _LI
 from neutron.agent.linux import ip_lib
@@ -189,6 +190,11 @@ def _delete_mac_spoofing_protection(vifs, current_rules):
 NAMESPACE = None
 
 
+@tenacity.retry(
+    wait=tenacity.wait_exponential(multiplier=0.01),
+    retry=tenacity.retry_if_exception(lambda e: e.returncode == 255),
+    reraise=True
+)
 def ebtables(comm):
     execute = ip_lib.IPWrapper(NAMESPACE).netns.execute
     return execute(['ebtables', '--concurrent'] + comm, run_as_root=True)