[submodule] Update submodule sonic-linux-kernel to the latest HEAD au…

…tomatically (sonic-net#16494)

#### Why I did it
src/sonic-linux-kernel
```
* fa40db7 - (HEAD -> master, origin/master, origin/HEAD) Change the system.map file permission only readable by root (sonic-net#329) (21 hours ago) [xumia]
```
#### How I did it
#### How to verify it
#### Description for the changelog