The vfs_unlink/d_delete functionality in the Linux VFS make the
dentry negative if it is the only inode being referenced. Case-insensitive
mode doesn't work with negative dentries, so if using CI-mode, invalidate
the dentry on unlink/rmdir.

SGI-PV: 983102
SGI-Modid: xfs-linux-melb:xfs-kern:31308a
Signed-off-by: NBarry Naujok <bnaujok@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@infradead.org>