quota: Split ->set_xstate callback into two

Split ->set_xstate callback into two callbacks - one for turning quotas
on (->quota_enable) and one for turning quotas off (->quota_disable). That
way we don't have to pass quotactl command into the callback which seems
cleaner.

Reviewed-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 227f37f..4da497b 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -371,13 +371,14 @@
 	int (*quota_on)(struct super_block *, int, int, struct path *);
 	int (*quota_on_meta)(struct super_block *, int, int);
 	int (*quota_off)(struct super_block *, int);
+	int (*quota_enable)(struct super_block *, unsigned int);
+	int (*quota_disable)(struct super_block *, unsigned int);
 	int (*quota_sync)(struct super_block *, 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 *, struct kqid, struct qc_dqblk *);
 	int (*set_dqblk)(struct super_block *, struct kqid, struct qc_dqblk *);
 	int (*get_xstate)(struct super_block *, struct fs_quota_stat *);
-	int (*set_xstate)(struct super_block *, unsigned int, int);
 	int (*get_xstatev)(struct super_block *, struct fs_quota_statv *);
 	int (*rm_xquota)(struct super_block *, unsigned int);
 };