net/mlx5e: Offload internal port as encap route device

When pefroming encap action, a route lookup is performed
to find the routing device the packet should be forwarded
to after the encapsulation. This is the device that has the
local tunnel ip address.

This change adds support to offload an encap rule where the
route device ends up being an ovs internal port.
In such case, the driver will add a HW rule that will encapsulate
the packet with the tunnel header and will overwrite the vport
metadata in reg_c0 to the internal port metadata value.
Finally, the packet will be forwarded to the root table to be
processed again with the indication that it came from an internal
port.

Signed-off-by: Ariel Levkovich <lariel@nvidia.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>