ocfs2: Support commit= mount option

Mostly taken from ext3. This allows the user to set the jbd commit interval,
in seconds. The default of 5 seconds stays the same, but now users can
easily increase the commit interval. Typically, this would be increased in
order to benefit performance at the expense of data-safety.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/ocfs2.h

@@ -229,6 +229,7 @@ struct ocfs2_super
 	wait_queue_head_t checkpoint_event;
 	atomic_t needs_checkpoint;
 	struct ocfs2_journal *journal;
+	unsigned long osb_commit_interval;
 
 	enum ocfs2_local_alloc_state local_alloc_state;
 	struct buffer_head *local_alloc_bh;