net/softnic: fix header size calculation

net/softnic: fix header size calculation

The rte_flow_item_eth and rte_flow_item_vlan items were updated in [1].
The rte_flow_item_ipv6 item was updated in [2].
The structs now contain additional metadata following the header data.
The size to use for match should be the header data size only, and
not the size of the whole struct.

This patch replaces the rte_flow_item_* with the corresponding rte_*_hdr.

Fixes: 09315fc83861 ("ethdev: add VLAN attributes to ethernet and VLAN items")
Fixes: ad976bd40d28 ("ethdev: add extensions attributes to IPv6 item")

Signed-off-by: Dekel Peled <dekelp@nvidia.com>
Acked-by: Jasvinder Singh <jasvinder.singh@intel.com>