net/i40e: fix VLAN offload setting issue

net/i40e: fix VLAN offload setting issue

When using kernel PF + DPDK VF, if setting VLAN strip on
or off in VF side after setting PVID for VF with ethtool in
PF side, it will cause VF Tx error. The root cause is that
Rx VLAN offload is not permitted after setting PVID for VF
in kernel PF side.
This patch fixes the issue by check VLAN offload capability
when setting VLAN offload.

Fixes: 5f0b95d59a98 ("net/i40e: support VLAN stripping for VF")
Cc: stable@dpdk.org
Signed-off-by: Beilei Xing <beilei.xing@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>