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

…sonic-net#16550)

#### Why I did it
src/dhcpmon
```
* 7c55e50 - (HEAD -> master, origin/master, origin/HEAD) Merge pull request #13 from jcaiMR/dev/jcai_master_interface_counter (7 days ago) [StormLiangMS]
* 085a087 - refine counting logic (10 days ago) [jcaiMR]
* de96a98 - Merge branch 'master' into dev/jcai_master_interface_counter (11 days ago) [jcaiMR]
* 5cb4468 - dhcp per-interface counter init commit (12 days ago) [jcaiMR]
```
#### How I did it
#### How to verify it
#### Description for the changelog