nfsd: note inadequate stats locking

After 89a26b3d "nfsd: split DRC global spinlock into per-bucket
locks", there is no longer a single global spinlock to protect these
stats.

So, really we need to fix that.  For now, at least fix the comment.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/netns.h

@@ -142,8 +142,11 @@ struct nfsd_net {
 	unsigned int             drc_hashsize;
 
 	/*
-	 * Stats and other tracking of on the duplicate reply cache. All of these and
-	 * the "rc" fields in nfsdstats are protected by the cache_lock
+	 * Stats and other tracking of on the duplicate reply cache.
+	 * These fields and the "rc" fields in nfsdstats are modified
+	 * with only the per-bucket cache lock, which isn't really safe
+	 * and should be fixed if we want the statistics to be
+	 * completely accurate.
 	 */
 
 	/* total number of entries */