In 2.6.32-358.123.2.openstack.el6 kernel (and I guess all openstack
kernels), the first field in the skb->cb is an offset field that is
used to calculate header length. In those kernels, skb->cb is a
structure of type skb_gso_cb with one field. Need to set that field
to zero.

BUG 1349560

Change-Id: Id61d9347fcda1fc639f7c2109223c10f918df12b