nfs: Add "lookupcache" to displayed mount options

Running "cat /proc/mounts" fails to display the "lookupcache" option.
This oversight cost me a bunch of wasted time recently.

The following simple patch fixes it.

CC: stable <stable@kernel.org>
Signed-off-by: NPatrick LoPresti <lopresti@gmail.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -655,6 +655,13 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
 
 	if (nfss->options & NFS_OPTION_FSCACHE)
 		seq_printf(m, ",fsc");
+
+	if (nfss->flags & NFS_MOUNT_LOOKUP_CACHE_NONEG) {
+		if (nfss->flags & NFS_MOUNT_LOOKUP_CACHE_NONE)
+			seq_printf(m, ",lookupcache=none");
+		else
+			seq_printf(m, ",lookupcache=pos");
+	}
 }
 
 /*