Inode: export symbol destroy_inode

To make sure we free the security data inodes need to be freed using
the proper VFS helper (which we also need to export for this). We mark
these inodes bad so we can skip the flush path for them.

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <david@fromorbit.com>