cifs: Treat unhandled directory name surrogate reparse points as mount directory nodes

If the reparse point was not handled (indicated by the -EOPNOTSUPP from
ops->parse_reparse_point() call) but reparse tag is of type name surrogate
directory type, then treat is as a new mount point.

Name surrogate reparse point represents another named entity in the system.

From SMB client point of view, this another entity is resolved on the SMB
server, and server serves its content automatically. Therefore from Linux
client point of view, this name surrogate reparse point of directory type
crosses mount point.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>