vfs_vnops.c: Modify the O_NAMEDATTR check for Solaris compatibility

[rmacklem]

Summary

The Solaris semantics for their O_XATTR flag is to use it
for a file object in the file system's namespace to indicate
that a named attribute for the file object should be open'd.

To do this, the O_NAMEDATTR flag must be allowed with a
non-named attribute directory. This patch changes vfs_vnops_cred()
to allow this.

This patch fixes 2ec2ba7e232d so that Solaris compatible
semantics can be implemented by patched ZFS code.

Test Plan

Tested with ZFS patched to support named attributes
in a Solaris compatible way.

[kib]

Could you, please, add the description of the behavior you aiming to in the patch, to the summary and commit message?

sys/kern/vfs_vnops.c

287–288

Why not remove the if () check there, and move the vp = XXX; goto bad; block under the prev. condition? There is only one possibility to get error != 0 there, after the removal of ENOENT.

[rmacklem]

Cleaned up the "if" as suggested by kib@.