[PATCH] ibmveth lockless TX

This patch adds the lockless TX feature to the ibmveth driver.  The
hypervisor has its own locking so the only change that is necessary is
to protect the statistics counters.

Signed-off-by: Santiago Leon <santil@us.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>