do not treat non-symlink reparse points as valid symlinks

Windows 8 and later can create NFS symlinks (within reparse points)
which we were assuming were normal NTFS symlinks and thus reporting
corrupt paths for.  Add check for reparse points to make sure that
they really are normal symlinks before we try to parse the pathname.

We also should not be parsing other types of reparse points (DFS
junctions etc) as if they were a  symlink so return EOPNOTSUPP
on those.  Also fix endian errors (we were not parsing symlink
lengths as little endian).

This fixes commit d244bf2d
which implemented follow link for non-Unix CIFS mounts

CC: Stable <stable@kernel.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>