ksmbd: fix null pointer dereference in alloc_preauth_hash()
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix null pointer dereference in alloc_preauth_hash()

The Client send malformed smb2 negotiate request. ksmbd return error
response. Subsequently, the client can send smb2 session setup even
thought conn->preauth_info is not allocated.
This patch add KSMBD_SESS_NEED_SETUP status of connection to ignore
session setup request if smb2 negotiate phase is not complete.