ocfs2: Enable cross extent block merge.

In ocfs2_figure_merge_contig_type, we judge whether there exists
a cross extent block merge and enable it by setting CONTIG_LEFT
and CONTIG_RIGHT accordingly.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>