mlxsw: spectrum_router: Use nexthop's scope to set action type

We currently use the scope of the FIB info to distinguish between a
direct unicast route and a gatewayed one. However, the kernel is
perfectly happy to configure a route with scope UNIVERSE to a directly
connected network.

Instead, we can rely on the first nexthop's scope to check if the route
is gatewayed or not.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>