[submodule] Update submodule sonic-linux-kernel to the latest HEAD automatically (#16931)

#### Why I did it
src/sonic-linux-kernel
```
* 6508505 - (HEAD -> master, origin/master, origin/HEAD) Add drop monitor Kernel Patches for buffer support (#338) (3 hours ago) [Vivek]
```
#### How I did it
#### How to verify it
#### Description for the changelog

Author: mssonicbld