Revert iptables TCP checksum-fill code

To fix bug 1722584 we inserted a checksum-fill rule for
metadata proxy replies.  Recent kernels have disabled
this support for TCP because it was invalid, and
supposedly not doing anything, so let's get ahead of
things and remove the code.

Kernel mailing list discussion is at
https://lore.kernel.org/patchwork/patch/824819/

Partially reverts ed1c3b0217

Depends-On: https://review.opendev.org/#/c/725213/
Change-Id: Ib7cc8f82a91972f17987fb95130edc4069d9423f
Related-bug: #1722584
(cherry picked from commit b1b8a438fe)
(cherry picked from commit 31320156e4)

neutron/agent/metadata/driver.py

@@ -193,14 +193,6 @@ class MetadataDriver(object):
                  {'interface_name': namespaces.INTERNAL_DEV_PREFIX + '+',
                   'port': port})]
 
-    @classmethod
-    def metadata_checksum_rules(cls, port):
-        return [('POSTROUTING', '-o %(interface_name)s '
-                 '-p tcp -m tcp --sport %(port)s -j CHECKSUM '
-                 '--checksum-fill' %
-                 {'interface_name': namespaces.INTERNAL_DEV_PREFIX + '+',
-                  'port': port})]
-
     @classmethod
     def _get_metadata_proxy_user_group(cls, conf):
         user = conf.metadata_proxy_user or str(os.geteuid())
@@ -294,8 +286,6 @@ def after_router_added(resource, event, l3_agent, **kwargs):
         router.iptables_manager.ipv4['filter'].add_rule(c, r)
     for c, r in proxy.metadata_nat_rules(proxy.metadata_port):
         router.iptables_manager.ipv4['nat'].add_rule(c, r)
-    for c, r in proxy.metadata_checksum_rules(proxy.metadata_port):
-        router.iptables_manager.ipv4['mangle'].add_rule(c, r)
     router.iptables_manager.apply()
 
     if not isinstance(router, ha_router.HaRouter):

neutron/tests/unit/agent/metadata/test_driver.py

@@ -52,13 +52,6 @@ class TestMetadataDriverRules(base.BaseTestCase):
             rules,
             metadata_driver.MetadataDriver.metadata_filter_rules(9697, '0x1'))
 
-    def test_metadata_checksum_rules(self):
-        rules = ('POSTROUTING', '-o qr-+ -p tcp -m tcp --sport 9697 '
-                 '-j CHECKSUM --checksum-fill')
-        self.assertEqual(
-            [rules],
-            metadata_driver.MetadataDriver.metadata_checksum_rules(9697))
-
 
 class TestMetadataDriverProcess(base.BaseTestCase):