net/mlx5: TC, Add support for SF tunnel offload

VF tunnel flow already exists and SF tunnel is the
same flow.  Support offloading of tunneling over SF device
by allow to attach an encap route over SF and set to use
indirect flow table on SF.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>