Add vhost TX offload (CSUM and TSO) support capabilities in vhost lib.
In order to support these features, and the following changes are added,
1. Extend 'VHOST_SUPPORTED_FEATURES' macro to add the offload features
negotiation.
2. Dequeue TX offload: convert the fileds in virtio_net_hdr to the
related fileds in mbuf.
Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
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