quota: move code from sync_quota_sb into vfs_quota_sync

Currenly sync_quota_sb does a lot of sync and truncate action that only
applies to "VFS" style quotas and is actively harmful for the sync
performance in XFS.  Move it into vfs_quota_sync and add a wait parameter
to ->quota_sync to tell if we need it or not.

My audit of the GFS2 code says it's also not needed given the way GFS2
implements quotas, but I'd be happy if this can get a detailed review.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/include/linux/quota.h b/include/linux/quota.h
index a6861f1..570348c 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -324,7 +324,7 @@
 struct quotactl_ops {
 	int (*quota_on)(struct super_block *, int, int, char *, int);
 	int (*quota_off)(struct super_block *, int, int);
-	int (*quota_sync)(struct super_block *, int);
+	int (*quota_sync)(struct super_block *, int, int);
 	int (*get_info)(struct super_block *, int, struct if_dqinfo *);
 	int (*set_info)(struct super_block *, int, struct if_dqinfo *);
 	int (*get_dqblk)(struct super_block *, int, qid_t, struct if_dqblk *);