Add regex check for gateway IP

Author: dvavili

contivModel.go

@@ -1864,6 +1864,11 @@ func ValidateNetwork(obj *Network) error {
 		return errors.New("encap string invalid format")
 	}
 
+	gatewayMatch := regexp.MustCompile("^((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])(\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])){3})?$")
+	if gatewayMatch.MatchString(obj.Gateway) == false {
+		return errors.New("gateway string invalid format")
+	}
+
 	if len(obj.NetworkName) > 64 {
 		return errors.New("networkName string too long")
 	}

network.json

@@ -36,6 +36,7 @@
 				},
 				"gateway": {
 					"type": "string",
+					"format": "^((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])(\\\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])){3})?$",
 					"title": "Gateway",
 					"showSummary": true
 				}