CVE-2026-31704 ksmbd: use check_add_overflow() to prevent u16 DACL size overflow

In the Linux kernel, the following vulnerability has been resolved: ksmbd: use checkaddoverflow to prevent u16 DACL size overflow setposixaclentriesdacl and setntacldacl accumulate ACE sizes in u16 variables. When a file has many POSIX ACL entries, the accumulated size can wrap past 65535, causin...