net/mlx5e: multipath, support routes with more than 2 nexthops

Today multipath offload is only supported when the number of
nexthops is 2 which block the use of it in case of system with
2 NICs.

This patch solve it by enabling multipath offload per NIC if
2 nexthops of the route are its uplinks.

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