vtnet(4) - disable TCP checksum offload by default
The existing TCP checksum offset for this driver causes ~95% retransmit rates for TCP IPv6 packets. This makes the driver effectively useless in its current state on IPv6 networks. Fixing the checksum offload code is beyond my expertise at this time, so we should at least disable the offload by default.
Patch for sys/dev/virtual/virtio/net/if_vtnet.c:
< static int vtnet_csum_disable = 0;
> static int vtnet_csum_disable = 1; //broken for IPv6, disable by default