[submodule] Update submodule linkmgrd to the latest HEAD automatically (

#19371)

#### Why I did it
src/linkmgrd
```
* d0124f5 - (HEAD -> master, origin/master, origin/HEAD) [active-standby] Fix default route handler race condition (#254) (3 days ago) [Longxiang Lyu]
```
#### How I did it
#### How to verify it
#### Description for the changelog