T5518: Add basic MLD support

Currently VyOS has `protocol igmp` option to enable IGMP querier and reports through FRR's pimd.

I would like to add support for IPv6 as well since FRR's IPv6 multicast functionality has significantly improved.

Enabling both MLD and IGMP on a VyOS router will allow us to turn on multicast snooping on layer-3 switches in dual-stack networks.

Example commands:

```
// Enable on interface eth0
set protocols pim6 interface eth0

// Explicitly join multicast group ff18::1234 on interface eth1
set protocols pim6 interface eth1 mld join ff18::1234

// Explicitly join source-specific multicast group ff38::5678 with source address 2001:db8::1 on interface eth1
set protocols pim6 interface eth1 mld join ff38::5678 source 2001:db8::1
```

1 files changed, 124 insertions, 0 deletions

diff --git a/smoketest/scripts/cli/test_protocols_pim6.py b/smoketest/scripts/cli/test_protocols_pim6.py
new file mode 100755
index 000000000..788329740
--- /dev/null
+++ b/smoketest/scripts/cli/test_protocols_pim6.py
@@ -0,0 +1,124 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2023 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+
+from base_vyostest_shim import VyOSUnitTestSHIM
+from vyos.configsession import ConfigSessionError
+from vyos.ifconfig import Section
+from vyos.utils.process import process_named_running
+
+PROCESS_NAME = 'pim6d'
+base_path = ['protocols', 'pim6']
+
+
+class TestProtocolsPIMv6(VyOSUnitTestSHIM.TestCase):
+    def tearDown(self):
+        # Check for running process
+        self.assertTrue(process_named_running(PROCESS_NAME))
+        self.cli_delete(base_path)
+        self.cli_commit()
+
+    def test_pim6_01_defaults(self):
+        # commit changes
+        self.cli_set(base_path)
+        self.cli_commit()
+
+        interfaces = Section.interfaces('ethernet')
+
+        # Verify FRR pim6d configuration
+        for interface in interfaces:
+            config = self.getFRRconfig(
+                f'interface {interface}', daemon=PROCESS_NAME)
+            self.assertIn(f'interface {interface}', config)
+            self.assertNotIn(f' ipv6 mld', config)
+
+    def test_pim6_02_mld_simple(self):
+        # commit changes
+        interfaces = Section.interfaces('ethernet')
+
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface', interface])
+
+        self.cli_commit()
+
+        # Verify FRR pim6d configuration
+        for interface in interfaces:
+            config = self.getFRRconfig(
+                f'interface {interface}', daemon=PROCESS_NAME)
+            self.assertIn(f'interface {interface}', config)
+            self.assertIn(f' ipv6 mld', config)
+            self.assertNotIn(f' ipv6 mld version 1', config)
+
+        # Change to MLD version 1
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface',
+                         interface, 'mld', 'version', '1'])
+
+        self.cli_commit()
+
+        # Verify FRR pim6d configuration
+        for interface in interfaces:
+            config = self.getFRRconfig(
+                f'interface {interface}', daemon=PROCESS_NAME)
+            self.assertIn(f'interface {interface}', config)
+            self.assertIn(f' ipv6 mld', config)
+            self.assertIn(f' ipv6 mld version 1', config)
+
+    def test_pim6_03_mld_join(self):
+        # commit changes
+        interfaces = Section.interfaces('ethernet')
+
+        # Use an invalid multiple group address
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface',
+                         interface, 'mld', 'join', 'fd00::1234'])
+
+        with self.assertRaises(ConfigSessionError):
+            self.cli_commit()
+        self.cli_delete(base_path + ['interface'])
+
+        # Use a valid multiple group address
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface',
+                         interface, 'mld', 'join', 'ff18::1234'])
+
+        self.cli_commit()
+
+        # Verify FRR pim6d configuration
+        for interface in interfaces:
+            config = self.getFRRconfig(
+                f'interface {interface}', daemon=PROCESS_NAME)
+            self.assertIn(f'interface {interface}', config)
+            self.assertIn(f' ipv6 mld join ff18::1234', config)
+
+        # Join a source-specific multicast group
+        for interface in interfaces:
+            self.cli_set(base_path + ['interface', interface,
+                         'mld', 'join', 'ff38::5678', '2001:db8::5678'])
+
+        self.cli_commit()
+
+        # Verify FRR pim6d configuration
+        for interface in interfaces:
+            config = self.getFRRconfig(
+                f'interface {interface}', daemon=PROCESS_NAME)
+            self.assertIn(f'interface {interface}', config)
+            self.assertIn(f' ipv6 mld join ff38::5678 2001:db8::5678', config)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)