CVE-2025-21815 mm/compaction: fix UBSAN shift-out-of-bounds warning

In the Linux kernel, the following vulnerability has been resolved: mm/compaction: fix UBSAN shift-out-of-bounds warning syzkaller reported a UBSAN shift-out-of-bounds warning of 1UL order in isolatefreepagesblock. The bogus compoundorder can be any value because it is union with flags. Add back...