app/testpmd: support VXLAN encap as sample action

app/testpmd: support VXLAN encap as sample action

Add support for rte_flow_action_vxlan_encap as a sample action.

The example of test-pmd command:

1.  set vxlan ip-version ... vni ... udp-src ...
    set raw_encap 1 eth src.../ ipv4.../...
    set sample_actions 2 vxlan_encap / port_id id 0 / end
    flow create 0 ... pattern eth / end actions
       sample ratio 1 index 2 / raw_encap index 1 / port_id id 0...

    The flow will result in all the matched egress packets will be
    encapsulated and sent to wire, and also mirrored the packets
    using VXLAN encapsulation data and sent to wire.

Signed-off-by: Salem Sol <salems@nvidia.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>