net/mlx5e: Don't block routes with nexthop objects in SW

net/mlx5e: Don't block routes with nexthop objects in SW

Routes with nexthop objects is currently not supported by multipath offload
and any attempts to use it is blocked, however this also block adding SW
routes with nexthop.

Resolve this by returning NOTIFY_DONE instead of an error which will allow such
a route to be created in SW but not offloaded.

This fix also solve an issue which block adding such routes on different devices
due to missing check if the route FIB device is one of multipath devices.

Fixes: 6a87afc072c3 ("mlx5: Fail attempts to use routes with nexthop objects")
Signed-off-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>