Support to enable and disable QINQ hardware strip, when configure VLAN
offload with QINQ strip mask. If there are packets have QINQ tag to RSS,
users should enable QINQ strip before configuring the RSS.
Fixes: 220b0e49bc47 ("net/txgbe: support VLAN")
Cc: stable@dpdk.org
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>