net/i40e: fix VLAN stripping in VF

net/i40e: fix VLAN stripping in VF

When VF adds VLAN, Linux PF driver enables VLAN stripping by default,
this might have issues if the app configured DEV_RX_OFFLOAD_VLAN_STRIP.

This behavior of the Linux driver causes confusion with the DPDK app
using i40e_pmd. So it is better to reconfigure the vlan_offload, which
checks for DEV_RX_OFFLOAD_VLAN_STRIP flag in the dev_conf and enables or
disables the vlan strip in the PF.

Application cannot use rte_eth_dev_set_vlan_offload() to set
the VLAN_STRIP, as this will only work for the first time when
original and current config mismatch, but for all subsequent call
it will be ignored.

Fixes: 4861cde46116 ("i40e: new poll mode driver")
Cc: stable@dpdk.org
Signed-off-by: Souvik Dey <sodey@rbbn.com>
Acked-by: Jeff Guo <jia.guo@intel.com>