ocfs2: Document /sys/fs/ocfs2

Add ABI documentation for these files:

	/sys/fs/ocfs2/max_locking_protocol
	/sys/fs/ocfs2/loaded_cluster_plugins
	/sys/fs/ocfs2/active_cluster_plugin
	/sys/fs/ocfs2/cluster_stack

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>