[submodule] Update submodule dhcpmon to the latest HEAD automatically (sonic-net#18273)

#### Why I did it
src/dhcpmon
```
* 22a7467 - (HEAD -> master, origin/master, origin/HEAD) Fix revert (#21) (9 hours ago) [kellyyeh]
* b1d890a - Revert DHCP Counter (#20) (24 hours ago) [kellyyeh]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld