ceph: request xattrs if xattr_version is zero

Following sequence of events can happen.
  - Client releases an inode, queues cap release message.
  - A 'lookup' reply brings the same inode back, but the reply
    doesn't contain xattrs because MDS didn't receive the cap release
    message and thought client already has up-to-data xattrs.

The fix is force sending a getattr request to MDS if xattrs_version
is 0. The getattr mask is set to CEPH_STAT_CAP_XATTR, so MDS knows client
does not have xattr.

Signed-off-by: Yan, Zheng <zyan@redhat.com>
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 12b2074..bbb44cd 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -714,7 +714,7 @@
 extern void ceph_queue_invalidate(struct inode *inode);
 extern void ceph_queue_writeback(struct inode *inode);
 
-extern int ceph_do_getattr(struct inode *inode, int mask);
+extern int ceph_do_getattr(struct inode *inode, int mask, bool force);
 extern int ceph_permission(struct inode *inode, int mask);
 extern int ceph_setattr(struct dentry *dentry, struct iattr *attr);
 extern int ceph_getattr(struct vfsmount *mnt, struct dentry *dentry,