__dev_queue_xmit  
   validate_xmit_skb
      netif_skb_features
           ndo_features_check
      validate_xmit_vlan
          vlan_hw_offload_capable   网卡是否支持vlan 加速 
              __vlan_hwaccel_push_inside  如果网卡不支持 “tx-vlan-offload” 把vlan直接插入包头，
      netif_needs_gso
          skb_gso_segment
      skb_needs_linearize
          __skb_linearize