[submodule] Update submodule sonic-dash-api/sonic-dash-api to the latest HEAD automatically (sonic-net#15725)

#### Why I did it
src/sonic-dash-api/sonic-dash-api
```
* 3f728d1 - (HEAD -> master, origin/master, origin/HEAD) Update vnet_direct in route.proto (#4) (11 days ago) [Ze Gan]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld