Restore GARP by default for floating IPs

Restore the default value of the send_arp_for_ha configuration
parameter to 3. This parameter was set to 0 by default to
prevent kernel crashes due to bug 1273386.

Change-Id: Idbdc6ff687734776ede45127878af6ad9b8b3ca1
Closes-Bug: 1317834

etc/l3_agent.ini

@@ -50,7 +50,7 @@
 
 # Send this many gratuitous ARPs for HA setup. Set it below or equal to 0
 # to disable this feature.
-# send_arp_for_ha = 0
+# send_arp_for_ha = 3
 
 # seconds between re-sync routers' data if needed
 # periodic_interval = 40

neutron/agent/l3_agent.py

@@ -164,7 +164,7 @@ class L3NATAgent(firewall_l3_agent.FWaaSL3AgentRpcCallback, manager.Manager):
                    help=_("TCP Port used by Neutron metadata namespace "
                           "proxy.")),
         cfg.IntOpt('send_arp_for_ha',
-                   default=0,
+                   default=3,
                    help=_("Send this many gratuitous ARPs for HA setup, if "
                           "less than or equal to 0, the feature is disabled")),
         cfg.StrOpt('router_id', default='',

neutron/tests/unit/test_l3_agent.py

@@ -50,7 +50,6 @@ class TestBasicRouterOperations(base.BaseTestCase):
         self.conf.set_override('router_id', 'fake_id')
         self.conf.set_override('interface_driver',
                                'neutron.agent.linux.interface.NullDriver')
-        self.conf.set_override('send_arp_for_ha', 1)
         self.conf.root_helper = 'sudo'
 
         self.device_exists_p = mock.patch(