ksmbd: fix use-after-free in smb_break_all_levII_oplock()
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free in smb_break_all_levII_oplock()

There is a room in smb_break_all_levII_oplock that can cause racy issues
when unlocking in the middle of the loop. This patch use read lock
to protect whole loop.