net/mlx5e: Use hint to resolve route when in HW multipath mode

As part of creating the tunnel headers while offloading TC encap rules,
we resolve the route and neighbour in order to get the source /
destination mac.

Since the way we offload multipath route is by having two HW rules,
one per uplink port, doing naive route lookup might get us a "wrong"
routing path which goes through the peer uplink and this will get us
eventually to create a wrong L2 header for the tunnel.

To avoid that, we use a device hint to get the correct route.

Signed-off-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>