[submodule] Update submodule dhcpmon to the latest HEAD automatically (…

…sonic-net#17730)

#### Why I did it
src/dhcpmon
```
* fc20a97 - (HEAD -> master, origin/master, origin/HEAD) [202311][counter] Clear counter table when dhcpmon init (#14) (2 hours ago) [Yaqiang Zhu]
```
#### How I did it
#### How to verify it
#### Description for the changelog