net/cxgbe: support flow API for matching QinQ VLAN

net/cxgbe: support flow API for matching QinQ VLAN

Add support to match fields in 802.1ad Q-in-Q VLAN packets.
Relax check for repeated pattern items for RTE_FLOW_ITEM_TYPE_VLAN
item, since the same item is used to represent both QinQ and VLAN
packets.

When QinQ match is enabled, the ethertype field in the hardware
spec must contain the innermost VLAN header's ethertype field,
and not the Ethernet header's ethertype field. The hardware
automatically searches for ethertype 0x88A8/0x8100 in Ethernet
header, when parsing incoming packet against QinQ/VLAN pattern,
respectively.

Signed-off-by: Karra Satwik <kaara.satwik@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>