btrfs: qgroup: inherit limit info from srcgroup in creating snapshot.

Currently, when we snapshot a subvol, snapshot will not copy the limits
from srcqgroup.

This patch make the qgroup in snapshot inherit the limit info when create
a snapshot.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 37188c6..34c2753 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2302,6 +2302,14 @@
 		dstgroup->excl_cmpr = level_size;
 		srcgroup->excl = level_size;
 		srcgroup->excl_cmpr = level_size;
+
+		/* inherit the limit info */
+		dstgroup->lim_flags = srcgroup->lim_flags;
+		dstgroup->max_rfer = srcgroup->max_rfer;
+		dstgroup->max_excl = srcgroup->max_excl;
+		dstgroup->rsv_rfer = srcgroup->rsv_rfer;
+		dstgroup->rsv_excl = srcgroup->rsv_excl;
+
 		qgroup_dirty(fs_info, dstgroup);
 		qgroup_dirty(fs_info, srcgroup);
 	}