CVE-2026-43376: ksmbd: fix use-after-free by using call_rcu() for oplock_info

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free by using callrcu() for oplockinfo

ksmbd currently frees oplockinfo immediately using kfree(), even though it is accessed under RCU read-side critical sections in places like opinfoget() and procshowfiles().

Since there is no RCU grace period delay between nullifying the pointer and freeing the memory, a reader can still access oplockinfo structure after it has been freed. This can leads to a use-after-free especially in opinfoget() where atomicincnotzero() is called on already freed memory.

Fix this by switching to deferred freeing using callrcu().