Thanks to Reuben Caron for pointing out on the OLPC developer’s mailing list that you can turn off the mesh networking using the following standard command:
echo 0 > /sys/class/net/eth1/lbs_mesh
This is nice because you probably just use regular wireless and don’t use or require mesh networking at all, so you might as well turn it off and save some power and complexity.
More details on the other ways you can control the mesh network via the firmware are in Trac.