ceph: no .snap inside of snapped namespace

Otherwise you can do things like

# mkdir .snap/foo
# cd .snap/foo/.snap
# ls
<badness>

Signed-off-by: Sage Weil <[e-mail]>

fs/ceph/dir.c

···
 
 	/* .snap dir? */
 	if (err == -ENOENT &&
+	    ceph_snap(parent) == CEPH_NOSNAP &&
 	    strcmp(dentry->d_name.name,
 		   fsc->mount_options->snapdir_name) == 0) {
 		struct inode *inode = ceph_get_snapdir(parent);