Previously, a single VLAN header is treated as inner VLAN,
but generally, a single VLAN header is treated as the outer
VLAN header.
The patch fixes the ether type of a single VLAN type, and
enables configuring inner and outer TPID for double VLAN.
Fixes: 19b16e2f6442 ("ethdev: add vlan type when setting ether type")
Signed-off-by: Beilei Xing <beilei.xing@intel.com>