Update gathering-information-for-troubleshooting-sites.mdx (#21493)

added mtr for tcp
ref: https://help.salesforce.com/s/articleView?id=001114985&type=1

Author: CFSeiya

src/content/docs/support/troubleshooting/general-troubleshooting/gathering-information-for-troubleshooting-sites.mdx

@@ -449,6 +449,12 @@ or with destination IP:
 mtr -rw <dest_IP> e.g.: mtr -rw 1.1.1.1
 ```
 
+with TCP port
+
+```sh
+mtr -P <tcp port> -T <destination ip>
+```
+
 Please refer to this documentation, which explains more about analysing MTR: [How to read MTR](https://www.cloudflare.com/en-gb/learning/network-layer/what-is-mtr/).
 
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