Added vni field in VRF Yang for VxLAN L3 VNI Support sonic-net#13456 (sonic-net#13735)

Why I did it
Added vni field in VRF Yang for VxLAN L3 VNI Support.

The VRF table schema as per EVPN HLD is below
https://github.com/sonic-net/SONiC/blob/master/doc/vxlan/EVPN/EVPN_VXLAN_HLD.md

Addresses Issue sonic-net#13456

Author: tapashdas

src/sonic-yang-models/doc/Configuration.md

@@ -1727,7 +1727,7 @@ table allow to change properties of a virtual router. Attributes:
 -   'ip_opt_action' contains packet action. Defines the action for
     packets with IP options
 -   'l3_mc_action' contains packet action. Defines the action for
-    unknown L3 multicast packets
+-   'vni' contains L3 VNI value. VNI associated Virtual router instance.
 
 The packet action could be:
 
@@ -1749,7 +1749,8 @@ The packet action could be:
 	'src_mac': '02:04:05:06:07:08',
 	'ttl_action': 'copy',
 	'ip_opt_action': 'deny',
-	'l3_mc_action': 'drop'
+	'l3_mc_action': 'drop',
+	'vni': '100'
 }
 ```
 

src/sonic-yang-models/tests/files/sample_config_db.json

@@ -2,6 +2,7 @@
     "SAMPLE_CONFIG_DB_JSON": {
         "VRF": {
                 "Vrf_blue": {
+                    "vni" : "100"
                 }
         },
         "DHCP_SERVER": {

src/sonic-yang-models/tests/yang_model_tests/tests/vrf.json

@@ -8,5 +8,12 @@
     },
     "VRF_TEST_WITH_FALLBACK": {
         "desc": "Configure VRF with fallback in VRF table."
+    },
+    "VRF_TEST_WITH_VNI": {
+        "desc": "Configure VRF with VNI in VRF table."
+    },
+    "VRF_TEST_WITH_VNI_OOR": {
+        "desc": "Configure VRF with out of range VNI in VRF table.",
+        "eStrKey": "Range"
     }
 }

src/sonic-yang-models/tests/yang_model_tests/tests_config/vrf.json

@@ -28,5 +28,27 @@
                 }]
             }
         }
+    },
+
+    "VRF_TEST_WITH_VNI": {
+        "sonic-vrf:sonic-vrf": {
+            "sonic-vrf:VRF": {
+                "VRF_LIST": [{
+                        "name": "Vrf_blue",
+                        "vni": "100"
+                }]
+            }
+        }
+    },
+
+    "VRF_TEST_WITH_VNI_OOR": {
+        "sonic-vrf:sonic-vrf": {
+            "sonic-vrf:VRF": {
+                "VRF_LIST": [{
+                        "name": "Vrf_blue",
+                        "vni": "16777216"
+                }]
+            }
+        }
     }
 }

src/sonic-yang-models/yang-models/sonic-vrf.yang

@@ -43,6 +43,14 @@ module sonic-vrf {
                         "Enable/disable fallback feature which is useful for specified VRF user to access internet through global/main route.";
                 }
 
+                leaf vni {
+                    type uint32 {
+                        range "0..16777215";
+                    }
+                    default 0;
+                    description
+                        "VNI mapped to VRF";
+                }
             } /* end of list VRF_LISt */
         } /* end of container VRf */
     } /* end of container sonic-vrf */