[submodule] Update submodule platform/vpp to the latest HEAD automatically (sonic-net#26914)

#### Why I did it
platform/vpp
```
* 4b1268d - (HEAD -> master, origin/master, origin/HEAD) Support test_drop_counters.py in Sonic-VPP (sonic-net#219) (5 days ago) [AkeelAli]
* 3de7f93 - Increase vpp dpdk tx buffer to handle burst (sonic-net#220) (7 days ago) [yue-fred-gao]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld