NFSv4: Ensure non-root user can trigger a referral automount

Currently only root can trigger a referral automount because only root
can access rpc_pipefs directories. Enabling read access to non-root
should be harmless (they can still not access the pipes themselves)
and will suffice to fix this problem.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/rpc_pipe.c

@@ -589,7 +589,7 @@ __rpc_mkdir(struct inode *dir, struct dentry *dentry)
 {
 	struct inode *inode;
 
-	inode = rpc_get_inode(dir->i_sb, S_IFDIR | S_IRUSR | S_IXUSR);
+	inode = rpc_get_inode(dir->i_sb, S_IFDIR | S_IRUGO | S_IXUGO);
 	if (!inode)
 		goto out_err;
 	inode->i_ino = iunique(dir->i_sb, 100);