net/mlx5e: TC, Restore tunnel info for sample offload

Currently the sample offload actions send the encapsulated packet
to software. sFlow expects tunneled packets to be decapsulated while
having the tunnel properties on the skb metadata fields.

Reuse the functions used by connection tracking to map the outer
header properties to a unique id. The next patch  will use that id
to restore the tunnel information of decapsulated packets onto the
skb.

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>