[submodule] Update submodule dhcpmon to the latest HEAD automatically (sonic-net#21792)

#### Why I did it
src/dhcpmon
```
* 8fface8 - (HEAD -> 202405, origin/202405) Merge pull request #33 from yaqiangz/202405_dhcpmon_bootp (2 minutes ago) [bingwang-ms]
* 5c98fd5 - Fix counting bootp packets by mistake (#31) (10 hours ago) [Yaqiang Zhu]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld