net/mlx5e: Maximize ip tunnel key usage on the TC offloading path

Use more fields out of the tunnel key (e.g the tunnel source IP address)
provided by upper layers for the route lookup done on the encap offload path.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Hadar Hen Zion <hadarh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>