netdev-offload-dpdk: Support vxlan encap offload with load actions.

netdev-offload-dpdk: Support vxlan encap offload with load actions.

Struct match has the tunnel values/masks in
match->flow.tunnel/match->wc.masks.tunnel.
Load actions such as load:0xa566c10->NXM_NX_TUN_IPV4_DST[],
load:0xbba->NXM_NX_TUN_ID[] are utilizing the tunnel masks fields,
but those should not be used for matching.
Offloading fails if masks is not clear. Clear it if no tunnel used.

Fixes: e8a2b5bf92bb ("netdev-dpdk: implement flow offload with rte flow")
Reviewed-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Gaetan Rivet <gaetanr@mellanox.com>
Acked-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Tested-by: Emma Finn <emma.finn@intel.com>
Signed-off-by: Lei Wang <leiw@mellanox.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>