execve updates for v7.1-rc1

- use strnlen() in __set_task_comm (Thorsten Blum)

- update task_struct->comm comment (Thorsten Blum)

sched: update task_struct->comm comment

Since commit 3a3f61ce5e0b ("exec: Make sure task->comm is always
NUL-terminated"), __set_task_comm() is unlocked and no longer uses
strscpy_pad() - update the stale comment accordingly.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20260401152039.724811-4-thorsten.blum@linux.dev
Signed-off-by: Kees Cook <kees@kernel.org>