net/mlx5e: TC, Support sample offload action for tunneled traffic

Currently the sample offload actions send the encapsulated packet
to software. This commit decapsulates the packet before performing
the sampling and set the tunnel properties on the skb metadata
fields to make the behavior consistent with OVS sFlow.

If decapsulating first, we can't use the same match like before in
default table. So instantiate a post action instance to continue
processing the action list. If HW can preserve reg_c, also use the
post action instance.

Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>