net/mlx5: add E-Switch VXLAN to validation routine

net/mlx5: add E-Switch VXLAN to validation routine

This patch adds VXLAN support for flow item/action lists validation.
The following entities are now supported:

- RTE_FLOW_ITEM_TYPE_VXLAN, contains the tunnel VNI

- RTE_FLOW_ACTION_TYPE_VXLAN_DECAP, if this action is specified
  the items in the flow items list treated as outer  network
  parameters for tunnel outer header match. The ethernet layer
  addresses always are treated as inner ones.

- RTE_FLOW_ACTION_TYPE_VXLAN_ENCAP, contains the item list to
  build the encapsulation header. In current implementation the
  values is the subject for some constraints:
    - outer source MAC address will be always unconditionally
      set to the one of MAC addresses of outer egress interface
    - no way to specify source UDP port
    - all abovementioned parameters are ignored if specified
      in the rule, warning messages are sent to the log

Minimal tunneling support is also added. If VXLAN decapsulation
action is specified the ETH item can follow the VXLAN VNI item,
the content of this ETH item is treated as inner MAC addresses
and type. The outer ETH item for VXLAN decapsulation action
is always ignored.

Suggested-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>