vfs_ceph: assert renameat() fsps match cwd

As discussed with Jeremy in bug 14232, the vfs_ceph.renameat_fn implementation currently ignores srcfsp and dstfsp. As a result, relative smb_fname_src/smb_fname_dest paths will be processed as relative to cwd. This is currently a valid assumption, as srcfsp and dstfsp should always match conn->cwd_fsp. Add an assert to clarify this.

Signed-off-by: David Disseldorp ddiss@samba.org