[sonic-config-engine]: Update L2 preset for dualtor (sonic-net#7215)

- When generating L2 preset, check for dual ToR setting from CLI option `-a '{"is_dualtor": true}'`
- When dual ToR is specified, add subtype field to DEVICE_METADATA table
- When dual ToR is specified, add MUX_CABLE, TUNNEL, LOOPBACK_INTERFACE, and PEER_SWITCH tables

Author: theasianpianist

src/sonic-config-engine/config_samples.py

@@ -1,5 +1,14 @@
+import sys
+
+from ipaddress import ip_interface
 from natsort import natsorted
 
+#TODO: Remove once Python 2 support is removed
+if sys.version_info.major == 3:
+    UNICODE_TYPE = str
+else:
+    UNICODE_TYPE = unicode
+
 def generate_t1_sample_config(data):
     data['DEVICE_METADATA']['localhost']['hostname'] = 'sonic'
     data['DEVICE_METADATA']['localhost']['type'] = 'LeafRouter'
@@ -39,11 +48,48 @@ def generate_empty_config(data):
     return new_data
 
 def generate_l2_config(data):
+    if 'is_dualtor' in data and data['is_dualtor']:
+        is_dualtor = True
+        data.pop('is_dualtor')
+    else:
+        is_dualtor = False
     data['VLAN'] = {'Vlan1000': {'vlanid': '1000'}}
     data['VLAN_MEMBER'] = {}
-    for port in natsorted(data['PORT']):
+    if is_dualtor:
+        data['DEVICE_METADATA']['localhost']['subtype'] = 'DualToR'
+        data['LOOPBACK_INTERFACE'] = {
+                                        'Loopback2': {},
+                                        'Loopback2|3.3.3.3': {}
+                                     }
+        data['MUX_CABLE'] = {}
+        data['PEER_SWITCH'] = {
+                                "peer_switch_hostname": {
+                                    "address_ipv4": "1.1.1.1"
+                                }
+                              }
+        data['TUNNEL'] = {
+                            "MuxTunnel0": {
+                                "dscp_mode": "uniform",
+                                "dst_ip": "2.2.2.2",
+                                "ecn_mode": "copy_from_outer",
+                                "encap_ecn_mode": "standard",
+                                "ttl_mode": "pipe",
+                                "tunnel_type": "IPINIP"
+                            }
+                         }
+
+        server_ipv4_base = ip_interface(UNICODE_TYPE('192.168.0.1/32'))
+        server_ipv6_base = ip_interface(UNICODE_TYPE('fc02:1000::1/128'))
+    for i, port in enumerate(natsorted(data['PORT'])):
         data['PORT'][port].setdefault('admin_status', 'up')
         data['VLAN_MEMBER']['Vlan1000|{}'.format(port)] = {'tagging_mode': 'untagged'}
+        if is_dualtor:
+            mux_cable_entry = {
+                'server_ipv4': str(server_ipv4_base + i),
+                'server_ipv6': str(server_ipv6_base + i),
+                'state': 'auto'
+            }
+            data['MUX_CABLE'][port] = mux_cable_entry
     return data
 
 _sample_generators = {