net/i40e: support TSO on tunneling packet

net/i40e: support TSO on tunneling packet

To enable Tx side offload on tunneling packet, driver should set
correct tunneling parameters: (1) EIPT, External IP header type;
(2) EIPLEN, External IP; (3) L4TUNT; (4) L4TUNLEN. This parsing
behavior is based on (ol_flag & PKT_TX_TUNNEL_MASK). And when
it's a tunneling packet, MACLEN defines the outer L2 header.

Also, we define TSO on each kind of tunneling type as a capabilities.
Now only i40e declares to support them.

Signed-off-by: Zhe Tao <zhe.tao@intel.com>
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>