btrfs: reorder btrfs_transaction members for better packing

	/* Be protected by fs_info->trans_lock when we want to change it. */

	enum btrfs_trans_state state;

	int aborted;

	struct list_head list;

	struct extent_io_tree dirty_pages;

	unsigned long start_time;

	struct list_head dirty_bgs;

	struct list_head io_bgs;

	struct list_head dropped_roots;

	unsigned int num_dirty_bgs;

	/*

	 * we need to make sure block group deletion doesn't race with

	 */

	struct mutex cache_write_mutex;

	spinlock_t dirty_bgs_lock;

	unsigned int num_dirty_bgs;

	/* Protected by spin lock fs_info->unused_bgs_lock. */

	struct list_head deleted_bgs;

	spinlock_t dropped_roots_lock;

	struct btrfs_delayed_ref_root delayed_refs;

	int aborted;

	struct btrfs_fs_info *fs_info;

};