We'll start noticing this with the next flag introduced as the lower
32bit are all used.
As this is old code we might need to do a full tree sweep one day, unless
changing our strategy to use a different `API' for getting/setting flags
along with the rest of the statfs data.
While here compare to 0 explicitly [1].
Suggested by: kib [1]
Reviewed by: kib
MFC after: 5 days
9df3a16421