vhost: check header for legacy dequeue offload
vhost: check header for legacy dequeue offload

When parsing the virtio net header and packet header for dequeue offload,
we need to perform sanity check on the packet header to ensure:
  - No out-of-boundary memory access.
  - The packet header and virtio_net header are valid and aligned.

Fixes: d0cf91303d73 ("vhost: add Tx offload capabilities")
Cc: stable@dpdk.org

Signed-off-by: Xiao Wang <28aecb4e45c1566b6185c24680691da84bd4fcf8@intel.com>
Reviewed-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk