fusefs: standardize on OPNOTSUPP for posix_fallocate(2)

[kevans]

Summary

POSIX Issue 7 had allowed EINVAL for this case, but issue 8 moves it
to ENOTSUP instead. ZFS uses the latter and we have some software in
ports already that's wanting to use that to detect the filesystem not
supporting it, so let's standardize on it.

[asomers]

You must also update the test cases in tests/sys/fs/fusefs/fallocate.cc . In particular, I think that the PosixFallocate.eopnotsupp will fail now, unless you update it.

[kevans]

Fix observed test failures; there's only a few places that we expect EINVAL.

[asomers]

sys/fs/fuse/fuse_vnops.c

666

I think you should also change this line to EOPNOTSUPP.

[kevans]

Correct it for the file-specific unsupported mode as well

+ Two more adjusted return values to fix the test

[kevans]

sys/fs/fuse/fuse_vnops.c

666

Bah, yes, sorry- not sure how I missed that one.