Btrfs: Include map_type in raid_bio

Corrent code use many kinds of "clever" way to determine operation
target's raid type, as:
  raid_map != NULL
  or
  raid_map[MAX_NR] == RAID[56]_Q_STRIPE

To make code easy to maintenance, this patch put raid type into
bbio, and we can always get raid type from bbio with a "stupid"
way.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 4313e8f..83069de 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -298,6 +298,7 @@
 	atomic_t refs;
 	atomic_t stripes_pending;
 	struct btrfs_fs_info *fs_info;
+	u64 map_type; /* get from map_lookup->type */
 	bio_end_io_t *end_io;
 	struct bio *orig_bio;
 	unsigned long flags;